I had assumed that, in perl, $x=(2,3,4,5) and ($x)=(2,3,4,5) would give me the same result, but was surprised at what happened in my tests. I am wondering why this behavior is the way it is and why wantarray behaves differently. Here are my tests and the results:
>perl -e '$x=(1,2,3,5);print("$x\n")'
5
>perl -e '($x)=(1,2,3,5);print("$x\n")'
1
>perl -e '$x=(wantarray ? (1,2,3,5) : 4);print("$x\n")'
4
>perl -e '($x)=(wantarray ? (1,2,3,5) : 4);print("$x\n")'
4
Is this behavior consistent/reliable across all platforms?
Whoops. wantarray is for context of subroutine calls...
>perl -e '$x=test();sub test{return(1,2,3,5)};print("$x\n")'
5
>perl -e '($x)=test();sub test{return(1,2,3,5)};print("$x\n")'
1
>perl -e '$x=test();sub test{return(wantarray ? (1,2,3,5) : 4)};print("$x\n")'
4
>perl -e '($x)=test();sub test{return(wantarray ? (1,2,3,5) : 4)};print("$x\n")'
1
So I guess it is consistent, but why does the list return the last value in scalar context?
So I guess it is consistent, but why does the list return the last value in scalar context?
Because it's useful.
my $x = f() || ( warn('!!!'), 'default' );
Well, more useful than any other alternative, at least. It's also consistent with its stronger cousin, ;.
sub f { x(), y(), z() };
is the same as
sub f { x(); y(); z() };
Each operator determines decides what it returns in both scalar and list context.[1]
There are operators that only even return a single scalar.
say time; # Returns the number of seconds since epoch
say scalar( time ); # Ditto.
But operators that normally returns more than one scalar and those that return a variable number of scalars cannot possible return that in scalar context, so they will return something else. It's up to each one to decide what that is.
say scalar( 4,5,6 ); # Last item evaluated in scalar context.
say scalar( @a ); # Number of elements in @a.
say scalar( grep f(), g() ); # Number of matching items.
say scalar( localtime ); # Formatted timestamp.
The list operator (e.g. x,y,z) returns what the last item of the list (z) returns when evaluated in scalar context. For example,
my $x = (f(),g(),@a);
is a weird way of writing
f();
g();
my $x = @a;
Notes