/*
SPEC:
CType inference occurs as part of the compile-time processing of a method invocation
and takes place before the overload resolution step of the invocation. When a
particular method group is specified in a method invocation, and no CType arguments
are specified as part of the method invocation, CType inference is applied to each
generic method in the method group. If CType inference succeeds, then the inferred
CType arguments are used to determine the types of formal parameters for subsequent
overload resolution. If overload resolution chooses a generic method as the one to
invoke then the inferred CType arguments are used as the actual CType arguments for the
invocation. If CType inference for a particular method fails, that method does not
participate in overload resolution. The failure of CType inference, in and of itself,
does not cause a compile-time error. However, it often leads to a compile-time error
when overload resolution then fails to find any applicable methods.
If the supplied number of arguments is different than the number of parameters in
the method, then inference immediately fails. Otherwise, assume that the generic
method has the following signature:
Tr M<X1...Xn>(T1 x1 ... Tm xm)
With a method call of the form M(E1...Em) the task of CType inference is to find
unique CType arguments S1...Sn for each of the CType parameters X1...Xn so that the
call M<S1...Sn>(E1...Em)becomes valid.
During the process of inference each CType parameter Xi is either fixed to a particular
CType Si or unfixed with an associated set of bounds. Each of the bounds is some CType T.
Each bound is classified as an upper bound, lower bound or exact bound.
Initially each CType variable Xi is unfixed with an empty set of bounds.
*/
// This file contains the implementation for method CType inference on calls (with
// arguments, and method CType inference on conversion of method groups to delegate
// types (which will not have arguments.)
////////////////////////////////////////////////////////////////////////////////
public static bool Infer(
ExpressionBinder binder,
SymbolLoader symbolLoader,
MethodSymbol pMethod,
TypeArray pClassTypeArguments,
TypeArray pMethodFormalParameterTypes,
ArgInfos pMethodArguments,
out TypeArray ppInferredTypeArguments)
{
Debug.Assert(pMethod != null);
Debug.Assert(pMethod.typeVars.size > 0);
Debug.Assert(pMethod.isParamArray || pMethod.Params == pMethodFormalParameterTypes);
ppInferredTypeArguments = null;
if (pMethodFormalParameterTypes.size == 0 || pMethod.InferenceMustFail())
{
return false;
}
Debug.Assert(pMethodArguments != null);
Debug.Assert(pMethodFormalParameterTypes != null);
Debug.Assert(pMethodArguments.carg <= pMethodFormalParameterTypes.size);
var inferrer = new MethodTypeInferrer(binder, symbolLoader,
pMethodFormalParameterTypes, pMethodArguments,
pMethod.typeVars, pClassTypeArguments);
bool success;
if (pMethodArguments.fHasExprs)
{
success = inferrer.InferTypeArgs();
}
else
{
success = inferrer.InferForMethodGroupConversion();
}
ppInferredTypeArguments = inferrer.GetResults();
return success;
}
////////////////////////////////////////////////////////////////////////////////
//
// In error recovery and reporting scenarios we sometimes end up in a situation
// like this:
//
// x.Foo( y=>
//
// and the question is, "is Foo a valid extension method of x?" If Foo is
// generic, then Foo will be something like:
//
// static Blah Foo<T>(this Bar<T> bar, Func<T, T> f){ ... }
//
// What we would like to know is: given _only_ the expression x, can we infer
// what T is in Bar<T> ? If we can, then for error recovery and reporting
// we can provisionally consider Foo to be an extension method of x. If we
// cannot deduce this just from x then we should consider Foo to not be an
// extension method of x, at least until we have more information.
//
// Clearly it is pointless to run multiple phases
public static bool CanObjectOfExtensionBeInferred(
ExpressionBinder binder,
SymbolLoader symbolLoader,
MethodSymbol pMethod,
TypeArray pClassTypeArguments,
TypeArray pMethodFormalParameterTypes,
ArgInfos pMethodArguments)
{
Debug.Assert(pMethod != null);
Debug.Assert(pMethod.typeVars.size > 0);
Debug.Assert(pMethodFormalParameterTypes != null);
Debug.Assert(pMethod.isParamArray || pMethod.Params == pMethodFormalParameterTypes);
// We need at least one formal parameter type and at least one argument.
if (pMethodFormalParameterTypes.size < 1 || pMethod.InferenceMustFail())
{
return false;
}
Debug.Assert(pMethodArguments != null);
Debug.Assert(pMethodArguments.carg <= pMethodFormalParameterTypes.size);
if (pMethodArguments.carg < 1)
{
return false;
}
var inferrer = new MethodTypeInferrer(binder, symbolLoader,
pMethodFormalParameterTypes, pMethodArguments, pMethod.typeVars, pClassTypeArguments);
return inferrer.CanInferExtensionObject();
}