NAME
Function::Return - specify a function return type
SYNOPSIS
use Function::Return;
use Types::Standard -types;
sub foo :Return(Int) { 123 }
sub bar :Return(Int) { 3.14 }
foo(); # 123
bar(); # ERROR! Invalid type
# multi return values
sub baz :Return(Num, Str) { 3.14, 'message' }
my ($pi, $msg) = baz();
my $count = baz(); # ERROR! Required list context.
# empty return
sub boo :Return() { return; }
boo();
DESCRIPTION
Function::Return allows you to specify a return type for your functions.
SUPPORT
This module supports all perl versions starting from v5.14.
IMPORT OPTIONS
no_check
You can switch off type check. If you change globally, use <$ENV{FUNCTION_RETURN_NO_CHECK}
>:
BEGIN {
$ENV{FUNCTION_RETURN_NO_CHECK} = 1;
}
use Function::Return;
sub foo :Return(Int) { 3.14 }
foo(); # NO ERROR!
And If you want to switch by a package, it is better to use the no_check option:
use Function::Return no_check => 1;
sub foo :Return(Int) { 3.14 }
foo(); # NO ERROR!
pkg
Function::Return automatically exports a return type by caller.
Or you can specify a package name:
use Function::Return pkg => 'MyClass';
ATTRIBUTES
Return
:Return
attribute is available.
FUNCTIONS
meta
This function lets you introspect return values:
use Function::Return;
use Types::Standard -types;
sub baz() :Return(Str) { 'hello' }
my $meta = Function::Return::meta \&baz; # Sub::Meta
$meta->returns->list; # [Str]
In addition, it can be used with Function::Parameters:
use Function::Parameters;
use Function::Return;
use Types::Standard -types;
fun hello(Str $msg) :Return(Str) { 'hello' . $msg }
my $meta = Function::Return::meta \&hello; # Sub::Meta
$meta->returns->list; # [Str]
$meta->args->[0]->type; # Str
$meta->args->[0]->name; # $msg
# Note
Function::Parameters::info \&hello; # undef
This makes it possible to know both type information of function arguments and return value at compile time, making it easier to use for testing etc.
METHODS
wrap_sub($coderef)
This interface is for power-user. Rather than using the :Return
attribute, it's possible to wrap a coderef like this:
my $wrapped = Function::Return->wrap_sub($orig, [Str]);
$wrapped->();
NOTE
enforce LIST to simplify
Function::Return
makes the original function is called in list context whether the wrapped function is called in list, scalar, void context:
sub foo :Return(Str) { wantarray ? 'LIST!!' : 'NON!!' }
my $a = foo(); # => LIST!!
The specified type checks against the value the original function was called in the list context.
wantarray
is convenient, but it sometimes causes confusion. So, in this module, we prioritize that it easy to understand the type of function return value.
requirements of type constraint
The requirements of type constraint of Function::Return
is the same as for Function::Parameters. Specific requirements are as follows:
> The only requirement is that the returned value (here referred to as $tc, for "type constraint") is an object that provides $tc->check($value) and $tc->get_message($value) methods. check is called to determine whether a particular value is valid; it should return a true or false value. get_message is called on values that fail the check test; it should return a string that describes the error.
compare Return::Type
Both Return::Type and Function::Return
perform type checking on function return value, but have some differences.
1. Function::Return
is not possible to specify different type constraints for scalar and list context, but Return::Type
is possible.
2. Function::Return
check type constraint for void context, but Return::Type
doesn't.
3. Function::Return
can be used together with Function::Parameters::Info
, but Return::Type
seems a bit difficult.
SEE ALSO
LICENSE
Copyright (C) kfly8.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
AUTHOR
kfly8 <kfly@cpan.org>