rs-0.10.0 — std.Error#

The built-in error families now have a namespace of their own, and families are raised by value everywhere, never by name as a string.

std.Error#

takepkg std.Error;

family ParseError(Error.Base){}

func m{
    run{ err(Error.RangeError, "too big"); } handle(Error.RangeError e){ out(e); }
    run{ x = 1 / 0; } handle(Error.Base e){ out(e); }       // RangeError: division by zero
}

std.Error exports Base, TypeError, RangeError, OutOfBoundsError, and SyntaxError. They are the interpreter's own families, not copies, so a handler for Error.RangeError catches a division by zero, and Error.TypeError is the same family as the bare TypeError, which keeps working without the import.

A family can extend one from a package#

family ParseError(Error.Base){} and family Timeout(net.NetworkError){} now work: a parent written as alias.Family is looked up in the packages the file imports. Before, only families declared in the same file and the bare built-in names could be parents.

Families are raised, not called#

err(TypeError, "message") raises; calling TypeError("message") now fails with a TypeError that says to use err. Previously it failed with "TypeError has no init and takes no arguments", and TypeError() with no arguments quietly built an error without a message. A family you declare with an init still constructs, and err(instance) raises it.

Changed#

• rs.core.raise takes a family, core.raise(RangeError, "message"), instead of its name as a string. It raises built-in families only; standard packages use it, and everything else uses err.
• A family prints as <family TypeError> rather than <func TypeError>.

Validation#

cargo test passes 114 tests (13 unit, 100 execution, 1 memory), with the new std.Error cases among them, on Windows Rust and on WSL-native Rust.