What does "if (1)" do?

Question

What does the syntax

if (1) {}

do?

I can't find documentation for this syntax and 1 is not being treated as a boolean. Am I right?.

Solution 1

Technically, the if (1) does nothing interesting, since it's an always-executed if-statement.

One common use of an if (1) though is to wrap code you'd like to be able to quickly disable, say for debugging purposes. You can quickly change an if (1) to if (0) to disable the code.

Solution 2

Yes, 1 is treated as true, so the block after if (1) is always executed.

From perldoc

The number 0, the strings '0' and "" , the empty list () , and undef are all false in a boolean context. All other values are true.

Solution 3

1 is indeed being treated as a boolean value in this case, which always evaluates to true.

This is basically an if statement which always passes (making it unnecessary in the first place).

Solution 4

When in doubt, use Deparse:

$ perl -MO=Deparse -e'if (1) {}'
do {
    ()
};
-e syntax OK

Solution 5

It runs the code block. It's equivalent to:

{
  ...
}

---

Added by ikegami:

No, it's not.

{ ... } is a "bare loop", a loop that executes only once. It is affected by next, last and redo.

if (1) { ... } is not a loop. It is not affected by next, last and redo.

>perl -E"for (1..3) { say $_; if (1) { next; } say $_; }"
1
2
3

>perl -E"for (1..3) { say $_; { next; } say $_; }"
1
1
2
2
3
3

However, they are similar in that both create a lexical scope.

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