sourceafIoc::Errs.fan

** Indicates the Err has a more interesting cause
@NoDoc
mixin Unwrappable {
    abstract Err? cause()
}

** As thrown by IoC
const class IocErr : Err, Unwrappable {
    internal new make(Str msg := "", Err? cause := null) : super(msg, cause) {}
}

** A generic helper Err thrown when a value is not found in an expected list of values.
** 
** This purposely does not extend `IocErr` so it may be freely used by other frameworks
const class NotFoundErr : Err {
    const Str[] values
    
    new make(Str msg, Obj?[] values, Err? cause := null) : super(msg + availableValues(values), cause) {
        this.values = values.exclude { it == null }.map { it.toStr }
    }

    Str availableValues(Obj?[] values) {
        vals := values.exclude { it == null }.map { it.toStr }.join(", ")
        return " Available values = ${vals}"
    }
}

** Thrown when an impossible condition occurs. You know when - we've all written comments like:
** 
** '// this should never happen...' 
const class WtfErr : Err {
    new make(Str msg, Err? cause := null) : super(msg, cause) {}
}