Lambda with default initializer gets called with random values instead

[dlangBugzillaToGithub]

Malte reported this on 2018-05-26T16:12:25Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=18909

CC List

• ag0aep6g
• Hiroki Noda

Description

The following code should print 2 but writes random numbers instead:

void main() @safe
{
    import std.stdio : writeln;

    writeln(identity(2));
}

int identity(immutable int q) pure nothrow @safe @nogc
{
    import std.algorithm : map;

    static immutable auto arr = [42];
    int getSecondArgument(int a, int b)
    {
        return b;
    }

    return arr.map!((int a, int b = q) => getSecondArgument(a, b))[0];
}

[dlangBugzillaToGithub]

ag0aep6g commented on 2018-05-26T16:37:31Z

Reduced Phobos away:

----
void main() @safe
{
    assert(identity(2) == 2); /* fails; should pass */
}

struct Map(alias fun)
{
    int front() @safe { return fun(); }
}

int identity(immutable int q) pure nothrow @safe @nogc
{
    int getArg(int b) @safe
    {
        return b;
    }
    return Map!((int b = q) => getArg(b))().front();
}
----

[dlangBugzillaToGithub]

kubo39 commented on 2019-04-27T07:53:53Z

This should fail to compile, and in this case you can use `lazy int b = q` and will work.