enforce/enforceEx overload for returntype

[dlangBugzillaToGithub]

admin (@Dav1dde) reported this on 2013-07-08T18:01:27Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=10576

CC List

• andrej.mitrovich (@AndrejMitrovic)

Description

auto foo() { int invalid_value = 3; return 3; }
auto result = enforceEx!(Exception, 3)(foo());

Currently this code doesn't work as expected:
auto result = enforceEx!Exception(foo() != 3);

result would be a boolean instead of the result of 3. If there is an overload which would take either a value to compare to or even a delagate (alias fun?) this would make enforceEx much more useful.

[dlangBugzillaToGithub]

andrej.mitrovich (@AndrejMitrovic) commented on 2013-07-08T18:09:20Z

What David means is he wants the ability to both return the value and throw if that value is invalid, however simply using (!value) as enforceEx currently does will not work properly with e.g. signed integers. For example:

-----
import std.exception;

int returnValid() { return 5; }
int returnInvalid() { return -1; }

void main()
{
    int x = enforceEx!Exception(returnValid());
    assert(x == 5);  // ok

    // this doesn't throw, but we want -1 to signal failure
    enforceEx!Exception(returnInvalid());

    // so as a workaround we use the check inline, however..
    int y = enforceEx!Exception(returnInvalid() != -1);

    // .. it is not useful for the return value since the value becomes a bool
    int z = enforceEx!Exception(returnValid() != -1);
    assert(z == 5);  // now this fails
}
-----