Ambiguous use of -CONSTANT resolved as -&CONSTANT()

Question

I'm trying to declare magic numbers as constants in my Perl scripts, as described in perlsub. However, I get warnings: ``` $ cat foo.perl use warnings ; use strict ; sub CONSTANT() { 5 } print 7-CONSTANT,"
" ; $ perl foo.perl Ambiguous use of -CONSTANT resolved as -&CONSTANT() at foo.perl line 3. 2 $ ``` The warning goes away if I insert a space between the minus and the `CONSTANT`. It makes the expressions more airy than I'd like, but it works. I'm curious, though: What is the ambiguity it's warning me about? I don't know any other way it could be parsed. (Perl 5.10.1 from Debian "squeeze").

Accepted Answer

First, some background. Let's look at the following for a second:

```
$_ = -foo;
```

`-foo` is a string literal[1].

```
$ perl -Mstrict -wE'say -foo;'
-foo
```

Except if a sub named `foo` has been declared.

```
$ perl -Mstrict -wE'sub foo { 123 } say -foo;'
Ambiguous use of -foo resolved as -&foo() at -e line 1.
-123
```

Now back to your question. The warning is wrong. A TERM (`7`) cannot be followed by another TERM, so `-` can't be the start of a string literal or a unary minus operator. It must be the subtraction operator, so there is no ambiguity.

This warning is still issued in 5.20.0[2]. I have filed a bug report.

Look ma! No quotes!

```
system(grep => ( -R, $pat, $qfn ));
```

Well, 5.20.0 isn't out yet, but we're in a code freeze running up to its release. This won't be fixed in 5.20.0.

Ambiguous use of -CONSTANT resolved as -&CONSTANT()

Solution

Problem