I know that it is possible to create a function within another function. Why might one need to do that in real life? (PHP)
function someFunction($var)
{
function anotherFunction()
{
return M_PI;
}
return anotherFunction();
}
The only time you'd ever really want to define a function inside of another function is if you didn't want that inner function available to anything until the outer function is called.
function load_my_library() {
...
function unload_my_library() {
}
}
The only time you'd need (or want) unload_my_library to be available is after the library has been loaded.
if (...) { function foo() { ... } }. Nesting this inside another function instead of an if may come in handy for code organization purposes. "Conditional functions" are handy in certain cases, one of the most used being the retrofitting of necessary functions into old PHP versions.Nested functions generally shouldn't ever be used. Classes and public/private methods solve the same sorts of problems much more cleanly.
However, function generating functions can be useful:
<?php
# requires php 5.3+
function make_adder($a)
{
return function($b) use($a) {
return $a + $b;
};
}
$plus_one = make_adder(1);
$plus_fortytwo = make_adder(42);
echo $plus_one(3)."\n"; // 4
echo $plus_fortytwo(10)."\n"; // 52
?>
This example is contrived and silly, but this sort of thing can be useful for generating functions used by sorting routines, etc.
I'm guessing here, but I believe that it is used for passing the function to another function for execution. For example, calling a search function where you can specify a callback function to perform the search order comparison. This will allow you to encapsulate the comparator in your outer function.
