/// <summary>
/// Tries to generate an instance shim mapping a concept method to
/// one on the given default struct.
/// </summary>
/// <param name="concept">
/// The concept containing the default struct.
/// </param>
/// <param name="conceptMethod">
/// The concept method we're implementing on an instance with a shim.
/// </param>
/// <param name="diagnostics">
/// A diagnostics set, to which we report default struct failures.
/// </param>
/// <returns>
/// Null if we couldn't synthesize a shim; otherwise, the created shim.
/// The shim might not be valid: this must be checked before acceptance.
/// </returns>
private SynthesizedDefaultShimMethod TrySynthesizeDefaultShim(NamedTypeSymbol concept, MethodSymbol conceptMethod, DiagnosticBag diagnostics)
{
var dstr = concept.GetDefaultStruct();
if (dstr == null)
{
return(null);
}
// Default-struct sanity checking
var conceptLoc = concept.Locations.IsEmpty ? Location.None : Locations[0];
var instanceLoc = Locations.IsEmpty ? Location.None : Locations[0];
if (dstr.Arity != 1)
{
// Don't use the default struct's location: it is an
// implementation detail and may not actually exist.
diagnostics.Add(ErrorCode.ERR_DefaultStructBadArity, conceptLoc, concept.Name, dstr.Arity, concept.Arity + 1);
return(null);
}
var witnessPar = dstr.TypeParameters[0];
if (!witnessPar.IsConceptWitness)
{
diagnostics.Add(ErrorCode.ERR_DefaultStructNoWitnessParam, conceptLoc, concept.Name);
return(null);
}
return(new SynthesizedDefaultShimMethod(conceptMethod, dstr, this));
}
