Dongbo Wang
aa0af5ed56
Refactor code to make it easier to maintain and a little faster. Changes are as follows:
1. Support finding a matching signature with variance. But make PowerShell prefer exact match over a match with variance.
2. The metadata signatures in `PSMethod<..>` are generated based on the array of method overloads in `MethodCacheEntry.MethodInformationStructures`, in the exact same order. So in `LanguagePrimitive.ConvertViaParseMethod`, when we try to figure out if there is a match using the metadata signatures in `PSMethod<..>`, we can get the index of the matching signature, and the same index should locate the matching method in `MethodCacheEntry.MethodInformationStructures`. Therefore, we don't need to compare signatures again in the actual conversion method, and instead, we can just leverage the index we found when figuring out the conversion in `ConvertViaParseMethod`.
- This gets rid of the reflection call `GetMethod("Invoke")` and the subsequent signature comparisons in the final conversion method.
- Also, when comparing signatures using `PSMethod<..>` in `ConvertViaParseMethod`, we can just use the generic argument types of each `Func<..>` metadata type, instead of calling `GetMethod("Invoke")` and then `GetParameters()`. This makes the code for comparing signatures simpler (the type `SignatureComparator`).
- Move `MatchesPSMethodProjectedType` from `PSMemberInfo.cs` to the type `SignatureComparator` in `LanguagePrimitives.cs`, as it's closely related to the signature comparison. Also, renamed it to `ProjectedTypeMatchesTargetType`.
- These changes make PSMethod-to-Delegate conversion a little faster, but no big improvement, as the true bottleneck probably is in delegate creation(?). Actually, the performance of this conversion is not critical at all at this moment because this feature should rarely be used in any hot script path. So this exercise is mainly for fun.
3. Remove `PSEnum<T>`. We can directly use enum types when constructing the metadata type `Func<..>`.
4. Remove the code that generates metadata signatures for generic method definitions (call `MakeGenericMethod` with fake types like `GenericType0`, `GenericType1`). This is because:
- We don't support convert generic method to delegate today, so may be better not spending time on preparing the metadata signature types for those methods.
- When the day comes that we need to support it, it's better to use generic argument types directly to construct the `Func<..>` metadata types. I left comments in `GetMethodGroupType` method in `PSMemberInfo.cs` to explain why that approach is better.
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