PHP: What are language constructs and why do we need them?

Question

I keep coming across statements like:

echo is a language construct but print is a function and hence has a return value

and

die is a language construct

My question is what are these language constructs and more importantly why do we need them?

Answer 1

Language constructs are hard coded into the PHP language. They do not play by normal rules.

For example, whenever you try to access a variable that doesn't exist, you'd get an error. To test whether a variable exists before you access it, you need to consult isset or empty:

if (isset($foo))

If isset was a normal function, you'd get a warning there as well, since you're accessing $foo to pass it into the function isset. Since isset is a language construct though, this works without throwing a warning. That's why the documentation makes a clear distinction between normal functions and language constructs.

Answer 2

Language constructs are what makes up the language: things like "if" "for" "while" "function" and so on.

The mentions in the PHP manual of things like "echo", "die" or "return" are there to make it clear that these are NOT functions and that they do not always behave like functions.

You could call "echo" as "echo()" so it may confuse beginners. That's why they put the clear disinction in the manual. To make it absolutely clear to everyone.

Other examples for language constructs that could be mistaken for functions are "array()", "list()" and "each()".

Answer 3

To understand the answer for this question you must understand how parsers work. A language is defined by syntax and the syntax is defined through keywords.

The language constructs are pieces of code that make the base of PHP language. The parser deals with them directly instead of functions.