PHP for Themers

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    Advanced Theming in Drupal 7
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    PHP for Themers
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    with James Walker
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    Before we get too far into our advanced theming,
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    I want to take a moment to review some PHP
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    topics that will aid us in doing the work that we've got ahead of us.
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    For those of you who've worked in PHP a lot
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    or feel comfortable with the language, most of this
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    should be review, but we're going to point out
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    some key things that you'll run into frequently
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    when doing advanced theme work.
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    First, we want to start with PHP data structures.
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    Most simply, we have variables.
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    Variables in PHP are prefixed with a dollar sign
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    and all variable names can only have alphanumeric characters--
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    that is alphabetical letters and numerals-- and underscores.
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    There will be two kinds of main data structures
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    that we'll be using in theming.
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    The first is arrays.
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    Arrays are generally lists that map values to keys.
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    They come in two variations.
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    The first is a simple vector array, which is just a list of values.
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    We've got an example here where we've got a simple array with two
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    elements, stingray and telescope.
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    In a simple vector array, the items are indexed
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    by integers beginning with zero.
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    So in this array, we have indexes of 0 and 1.
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    The other common format of arrays in PHP
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    are hash tables or associative arrays.
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    These arrays are indexed by strings or other values
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    not necessarily 0, 1, et cetera.
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    So in our example here, we have an array of cherries and apple
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    with the indexes of red and green.
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    When working with arrays, we'll frequently
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    want to reference certain items that are part of the array.
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    So in our stingray and telescope array example,
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    if we wanted to print out the first item
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    we could reference that by using $stuff and then square brackets
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    around the index, such as 0.
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    Printing that value would give us the string stingray.
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    In a hash table example, we use the same method,
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    but using the key string rather than the integer index.
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    So here for our fruit array, if we print
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    fruit and then green in square brackets,
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    we will get the value apple.
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    The other data structure that we'll see frequently in Drupal theming
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    are objects.
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    Objects have properties that are similar to elements of an array.
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    The syntax is slightly different, though.
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    To reference an object property we use
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    the arrow notation, which is created by a dash and an angle bracket.
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    So as you can see here, we have a robot
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    object that has three properties-- color, material, and finish.
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    Objects in PHP are similar to arrays, the main difference
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    being that they can have methods or functions associated with them.
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    Primarily in theming we'll be just concerned with object properties.
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    In a more complex example, something that we may actually
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    run into in Drupal theming, we'll see
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    that we can chain these things together to get
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    quite complicated data structures.
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    So in our first example, we're printing the nodes links item.
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    So we're starting with we have a node object
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    in which we're referencing a certain property known as links.
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    Links is actually a two-dimensional array where we have
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    first a key of blog_usernames_blog.
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    And then within that, we have an href key.
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    We can see that value prints out blog slash one, which is the URL
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    for an individual user's blog.
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    The next topic we want to cover are conditionals.
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    We'll frequently see these to apply certain display
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    logic, only printing things when certain conditions apply.
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    The most common conditional structure that we'll see
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    is the if else statements.
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    So our example here reads that if a is equal to b,
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    it'll print "it's equal."
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    If the values of a and b aren't equal,
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    then it'll check the next conditional, which
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    is the else if a is less than b.
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    So if the value of a is in fact less than b,
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    then we will print "it's smaller."
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    Finally, if none of the previous conditions are true,
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    we'll fall back to the else statement, which will
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    just print the text "who knows."
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    The if else statements in PHP have a couple of syntax variations
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    that you'll frequently run into in Drupal themes.
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    The first is a colon notation, where again, the logic is the same.
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    We're saying if a is equal to b, then print "it's equal,"
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    otherwise end the statement.
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    The nice thing about this syntax that we'll see frequently in themes
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    is that we can break this syntax up and include
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    some markup in the middle.
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    We'll see examples of that in most template files.
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    The other variation that we'll see is a nice shorthand,
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    if you just have a small conditional that you want to only take up
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    one line.
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    In this syntax, we have our action first.
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    So print is what we want to ultimately do with the value.
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    Then we have our conditional.
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    So if this evaluates to true, then we want to print
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    the part after the question mark.
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    If the conditional is not true, then our else statement
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    is signified by the colon.
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    So what this conditional is doing is if a is equal to b, then
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    it will print "it's equal."
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    Otherwise, it will print nothing.
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    A slightly more complicated version of this conditional
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    is the switch statement.
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    This is something we'll also see in template.php files from time
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    to time.
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    Essentially, switch is a shorthand for very long if and else if
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    statements.
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    In this example here, we're going to switch our cases based on the value
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    of the time of day variable.
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    And what the switch statement is going
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    to do is based on the value of that variable,
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    it's going to look for matching cases.
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    So in the first block we have the case morning.
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    So if time of day is equal to morning,
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    then it'll print "eat breakfast."
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    The second case is of afternoon.
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    So if time of day is not equal to morning,
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    then it'll move on and check to see if time of day
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    is equal to afternoon.
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    If that's true, then it'll print "lunch time."
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    Finally, much like an else clause, if none of the previous conditions
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    evaluate, than the default syntax can be used, in which case
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    it'll just print Zs.
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    Important to note in switch statements
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    is that you can have multiple cases that may match,
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    which is why we make use of the break statement.
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    So if we want only morning to be applied,
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    we will break after the print "east breakfast."
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    Now let's talk about loops.
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    We use loops in PHP when we want to execute a certain segment of code
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    multiple times in a row.
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    Just like conditional statements, loops
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    have a couple different syntax variations in PHP.
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    The first of these is known as a while loop.
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    In a while loop we're going to have a single condition that will be
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    checked on each iteration of the loop,
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    whether or not the condition still evaluates to true.
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    So in our example here, we have a simple counter variable called i,
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    and as we go through the loop each iteration
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    through the loop the condition's going to be checked
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    to see if I is still less than 10.
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    If that's true, then it will execute the code that will print
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    "Lullabot loves you" followed by a shorthand
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    for incrementing the value of i.
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    So on the first run i will be equal to zero,
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    which is, in fact, less than 10.
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    So "Lullabot loves you" will print, and then
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    i's value will be updated to 1.
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    PHP will then return to the top, check to see that i is
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    still less than 10, and continue.
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    The result will be that "Lullabot loves you"
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    will be printed 10 times in a row.
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    The same structure has an alternate syntax known as a for loop.
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    In for loops, we get a special sort of condition that has three
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    parts separated by semicolons.
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    The first is that initial condition, which is i equals 0,
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    followed by the conditional or the test
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    to check to see if it's still true, followed
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    by a statement to increment the counter, generally.
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    So this for loop functions in the exact same way
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    as the previous while loop.
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    Our i counter begins at 0 and each iteration through the loop
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    is updated by one until it is equal to 10.
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    So we get the exact same result.
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    Lullabot loves you is printed 10 times.
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    Final variation on looping syntax is known as foreach.
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    Foreach is handy if we have an array full of items
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    that we wanted execute some code on each element in the array.
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    So in this example we're going to loop through our stuff array
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    and print each item in that array.
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    So if we recall our original stuff array,
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    we'll get stingray printed by telescope.
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    We can clean this up slightly and add in a br tag, for example,
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    and that'll change our output to be stingray and telescope.
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    Finally we'd like to talk about functions.
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    As we get into more advanced theming topics,
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    we're going to be writing a lot of functions
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    to implement certain hooks inside of Drupal's theme system.
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    Let's have a look at how they're constructed in PHP.
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    Functions in PHP are used to encapsulate
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    frequently repeated tasks.
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    We'll be writing lots of functions as we
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    start to override Drupal theme functions
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    and implement preprocess hooks.
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    The structure of a function begins with the word function,
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    so that we know we're beginning a new function declaration.
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    Then we give a name to our function.
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    In this case, my_function.
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    And then we pass in a list of parameters, which will be
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    the input values to our function.
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    In the case in this example, we have the variable a and b.
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    Finally, a function can optionally have a return
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    value that it provides as output.
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    In this case, we'll be outputting the value of the variable c.
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    There's a couple interesting things to note
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    when working with functions.
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    First off, we can pass any values into the a and b parameters.
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    They can be variables that aren't named a or b, or static values.
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    The other thing to note is that we can have variables that
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    exist only inside the scope of our function, such as the variable c,
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    here.
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    The variable c only exists inside the execution of my_function.
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    Let's have a look at how our example function will behave when used.
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    The bottom here, we have a variable x that we're setting equal to 4
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    and then calling print my_function with the variable x passed
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    as the first parameter and the number
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    6 passed as the second parameter.
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    Inside of my function's call now the variable a
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    will be equal to the variable x, which
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    is going to be the value of 4.
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    The parameter b will be equal to the number 6.
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    So we'll see that c is going to get set to 4 plus 6, which is 10,
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    and then that value will be returned.
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    So the result of print my_function will be the number 10.
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    Also inside of our function we have the value
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    of a being set to a plus 1.
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    So inside of the function, the value of a will be five.
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    However, that a variable only exists inside the scope of our function.
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    Thus when we print x after our function call,
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    it's still equal to the number 4.
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    In PHP we can also pass parameters by a reference.
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    We can see this in the syntax by the addition of the ampersand
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    before the parameter a.
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    This will change the behavior of our function slightly when called.
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    If we look at our previous example again, where we have the variable x
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    equal to 4, the first print statement
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    that's printing the result of my function
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    will still be 4 plus 6, which is the value
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    of c, so it'll still print 10.
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    However, because our x variable has now been passed by a reference,
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    any changes that happen inside the body of our function
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    will actually persist after the call has been made.
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    So when we take x and refer to it as a inside of the function,
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    and we do a equals a plus one, that will
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    actually change the value of the x variable from the calling scope.
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    So when we print the x variable after the call to my_function,
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    that variable will now print out the value 5.
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    While we don't have time in this video to cover everything
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    that there is to know about PHP, we hope a few of these simple pointers
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    will help make some of the code that we'll be looking
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    at later make a little bit more sense to those of you
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    who are newer to PHP.
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    If you're looking for more information
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    or want to learn more about PHP, PHP.net
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    is a great resource that fully documents the entire language.

Advanced Theming for Drupal 7

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PHP for Themers

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13 minutes 57 seconds // Drupal 7 // HDCC //

Before we dive into advanced theming we are going to review the basic PHP you will need to use. This is a short review of PHP, including topics like data structures (arrays and objects), conditionals and operators, loops, and functions.

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