On Thursday, 24 September 2020 at 02:28:11 UTC, Paul Backus wrote:
SumType is a generic sum type for modern D. It is designed to
be an improved
alternative to `std.variant.Algebraic`.
Features:
- Pattern matching, including:
- Match-by-introspection ("if it compiles, it matches") (★)
- Multiple dispatch (★)
- Support for self-referential types (`This`).
- Works with `pure`, `@safe`, `@nogc`, `nothrow`, and
`immutable` (★)
- Compatible with `-betterC` and `-dip1000` (★)
- Zero runtime overhead compared to hand-written C
- No heap allocation
- Does not rely on runtime type information (`TypeInfo`)
(★)
Starred features (★) are those that are missing from
`Algebraic`.
The big new feature in this release is multiple dispatch: you
can pass multiple
SumType arguments to a single `match` call, and it will pass
each of those
SumTypes' values as a separate argument to the selected handler.
If you're used to calling `match` with UFCS, the syntax for
passing multiple
arguments may take some getting used to. I recommend the
following idiom:
bool sameDimensions(Point p1, Point p2)
{
// Set up your handlers first
alias doMatch = match!(
(Point2D _1, Point2D _2) => true,
(Point3D _1, Point3D _2) => true,
(_1, _2) => false
);
// Now make the actual call
return doMatch(p1, p2);
}
Other improvements since 0.9.0, the last announced version:
- SumTypes can be used as keys in associative arrays
- isSumType!T is now true if T implicitly converts to a
SumType
- sumtype's license has been changed from MIT to Boost 1.0
- Member types with non-const `opEquals` overloads finally
work correctly
- Various other bug fixes and documentation improvements
Links:
- Documentation:
https://pbackus.github.io/sumtype/sumtype.html
- DUB: https://sumtype.dub.pm
- Github: https://github.com/pbackus/sumtype
Hello,
Older version of sumtype accept this code:
void main(){
import sumtype;
alias Val = SumType!(bool);
const bool b = true;
Val val = b; //fail in newest version
val = b; //fail in newest version
}
but new version need exact type:
void main(){
import sumtype;
alias Val = SumType!(bool);
bool b = true; //cannot be const
Val val = b;
val = b;
}
is it bug in new version or old version?
