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Closed 11 years ago.
Possible Duplicate:
Immediately executing anonymous functions
I want to immediately evaluate an anonymous function rather than it appearing as a Closure object in method args. Is this possible?
For example:
$obj = MyClass;
$obj->Foo(function(){return "bar";}); // passes a Closure into Foo()
$obj->Foo(function(){return "bar";}()); // passes the string "bar" into Foo()?
The 3rd line is illegal syntax -- is there any way to do this?
Thanks
You could do it with call_user_func ... though that might be a bit silly when you could just assign it to a variable and subsequently invoke the variable.
call_user_func(function(){ echo "bar"; });
You might think that PHP 5.4 with it's dereferencing capabilities would make this possible. You'd be wrong, however (as of RC6, anyway).
Related
This question already has answers here:
Should an array be declared before using it? [closed]
(7 answers)
Closed 7 years ago.
In most languages, I have to initialize an associative array before I can use it:
data = {}
data["foo"] = "bar"
But in PHP I can just do
data["foo"] = "bar"
Are there any repercussions to doing this? Is this "the right way" to write PHP?
Is the same, but is not a good idea, the next is a copy-paste from php documentation.
If $arr doesn't exist yet, it will be created, so this is also an alternative way to create an array. This practice is however discouraged because if $arr already contains some value (e.g. string from request variable) then this value will stay in the place and [] may actually stand for string access operator. It is always better to initialize variable by a direct assignment.
Basically it's the same, and no you won't find any problem or repercussion.
But if you like you can do this:
$a = array();
You can read more in the PHP page
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Reference Guide: What does this symbol mean in PHP? (PHP Syntax)
(24 answers)
Closed 8 years ago.
Can you please explain to me the differences between two functions:
function &a(){
return something;
}
and
function b(){
return something;
}
Thanks!
The first returns a reference to something, the second a copy of something.
In first case, when the caller modify the returned value, something will be modified as a global variable do.
In the second case, modifying a copy as no effect to the source.
An ampersand before a function name means the function will return a reference to a variable instead of the value.
According to this LINK
Returning by reference is useful when you want to use a function to find to which
variable a reference should be bound. Do not use return-by-reference to increase
performance. The engine will automatically optimize this on its own. Only return
references when you have a valid technical reason to do so.
This question already has answers here:
What is the difference between a language construct and a "built-in" function in PHP?
(4 answers)
Closed 8 years ago.
PHP has a large number of batteries-included functions, e.g. functions on arrays. Some of these, like each, are present in get_defined_functions()['internal']. Others, like reset and many others, are not present at all. However, they are treated as functions in every other way: they are not documented as "language constructs" or keywords; I can call them using the "variable function" feature; function_exists("reset") returns true; if I try to redefine them (e.g. function reset() { ... }), I get an error about redeclaration, rather than a syntax error; and so on.
Why are these functions not listed by get_defined_functions? Are they not actually functions? If not, what are they? If they are functions, then what actually is it that get_defined_functions is listing? In either case, how do I list the things that don't appear in get_defined_functions?
Quite a short answer: Reset is present in get_defined_functions()['internal'].
Look at [1532] in this fiddle: http://phpfiddle.org/main/code/h5n-ndx
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
What is the difference between a language construct and a “built-in” function in PHP?
I have read that in php programming book "Language construct such asecho()andisset()can not be called through variable function"
What is the meaning of it ?
echo() and isset() (just to pick those exemplary for other PHP language constructs) can't be called in a variable function.
Here comes an example of a variable function.
function foo() {
echo "foo";
}
$func1 = 'foo';
$func1(); // "foo" will be output
And now let's try with echo:
$func2 = 'echo';
$func2(); // "Fatal error: Call to undefined function echo() on line 10"
That's because echo() isn't a function, but a language construct.
Any function in php, whether it is built-in or user function, it all will store in an HashTable in the php internal.
When you call a function, It find the function on the HashTable by function name.
But echo(), isset() isn't function, so it's not exists in the function HashTable. so "Language construct such asecho()andisset()can not be called through variable function"
It means you cannot do this:
$f = 'echo';
$f('hello world');
Because echo is not a function (like sprintf for example) but a language symbol (like if for example)
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Parse error on explode('-','foo-bar')[0] (for instance)
In PHP there are functions that return an array, for example:
$a = parse_url("https://stackoverflow.com/q/9461027/87015");
echo $a["host"]; // stackoverflow.com
My question is how to combine the above two statements into a single statement. This (is something that works in JavaScript but) does not work:
echo parse_url("https://stackoverflow.com/q/9461027/87015")["host"];
Note: function array dereferencing is available since PHP 5.4; the above code works as-is.
You can do a little trick instead, write a simple function
function readArr($array, $index) {
return $array[$index];
}
Then use it like this
echo readArr(parse_url("http://stackoverflow.com/questions/9458303/how-can-i-change-the-color-white-from-a-uiimage-to-transparent"),"host");
Honestly, the best way of writing your above code is:
$a = parse_url("http://stackoverflow.com/q/9461027/87015");
echo $a["scheme"];
echo $a["host"];
Isn't that what I originally posted?
Yes. Depending on context you may want a better name than $a (perhaps $url), but that is the best way to write it. Adding a function is not an attractive option because when you revisit your code or when someone reads your code, they have to find the obscure function and figure out why on earth it exists. Leave it in the native language in this case.
Alternate code:
You can, however, combine the echo statements:
$a = parse_url("http://stackoverflow.com/q/9461027/87015");
echo $a['scheme'], $a['host'];