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Constant Folding

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Constant Folding

Like C, Perl does a certain amount of expression evaluation at compile time, whenever it determines that all of the arguments to an operator are static and have no side effects. In particular, string concatenation happens at compile time between literals that don't do variable substitution. Backslash interpretation also happens at compile time. You can say

    'Now is the time for all' . "\n" .
        'good men to come to.'

and this all reduces to one string internally. Likewise, if you say

    foreach $file (@filenames) {
        if (-s $file > 5 + 100 * 2**16) { ... }
    }

the compiler will precompute the number that expression represents so that the interpreter won't have to.

Source: Perl operators and precedence
Copyright: Larry Wall, et al.

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