gistfile1.pl

#这个问题解决了：
#Most of the power comes from the implicit smartmatching
#that can sometimes apply. Most of the time, when(EXPR) is
#treated as an implicit smartmatch of $_ , that is, $_ ~~ EXPR .
#(See Smartmatch Operator in perlop for more information on smartmatching.)
#But when EXPR is one of the 10 exceptional cases 
#(or things like them) listed below, it is used directly as a boolean.

#1.  A user-defined subroutine call or a method invocation.
#其他省略

use MooseX::Declare;
class Class {
    has 'num' => (
        is      => 'rw',
        isa     => 'Num',
        default => 123,
    );
}

my $e = Class->new;

sub return_123 { return 123; }

use 5.010;
given (124) {
    when ( $e->num ) { say "123"; }    #实际执行这里
    when (124)       { say "124"; }    #应该执行这个
}

given (124) {
    when ( return_123() ) { say "123"; }    #实际执行这里
    when (124)            { say "124"; }    #应该执行这个
}

given (124) {
    when ( return_123() . "" ) { say "123"; }
    when (124)                 { say "124"; }    #正确执行到这里
}

given (124) {
    when ( my $x = $e->num ) { say "123"; }
    when (124) { say "124"; }                    #这次就执行了这个
}

#这个问题定位在smart matching上么;
if ( 124 ~~ return_123() ) {
    print "get in if";                           #X不能执行到这里
}

given(123){
    when(1 == 1) {say "1 == 1";}
    when(123) {say "123";}
}