cgen of match expr

[danieldaeschle]

Currently cgen uses C ternary expression to generate a match expression which returns a value. The disadvantage of the ternary operator is, that it doesn't support variables which results in no it variable on SumTypes and in general no variables in the body.

Not working example:

// sumtype
a := match b {
    c { it.foo }
    else { placeholdervalue }
}

The solution for this would be to use common if-else generation.
There is another Problem with this.
Let's say, the match expr assigns the result to a variable.
Then cgen generates an output of string myRes =. After this output comes the ternary operator, normally.
To return something using if and else we have to use a temp-variable. But because our myRes variable is defined before, there is no way to assign the value to it.

The perfect result of a match-expr would look like this:

#line
temp_type tmp; if (cond) { 
  ...
  tmp = ...
#line
}
#line
else {
  ...
  tmp = ...
#line
} final_type final = tmp;

Currently there is no way to get this result.

This should work:

type Abc = int | string

struct Foo {
    bar string
}

fn foo(bar string) {}

fn main() {
    a := Abc(1)
    len := match a {
        int { 'asdsad' }
        string { a }
    }

    x := Foo{
        bar: match a {
            int { 'asdsad' }
            string { a }
        }
    }

    // vlib/time/format.v:140
    foo(match a {
        int { 'asdsad' }
        string { a }
    })
}

[danieldaeschle]

the example works somehow no :)