Reflection caching

[bugproof]

Reflection is slow, why isn't it internally cached by default?

[mattwarren]

There's is already some caching, for instance if you fetch a single field/property/method all the other fields/properties/methods on the Type are cached internally.

This is done using RuntimeTypeCache (here) and this search shows you the places in the code that make use of it.

There's other things going on with reflection that also contribute to the overhead, this post explains some of them

[jkotas]

What are the specific reflection operations you would like to run faster?

[bugproof]

GetCustomAttributes, getting and setting values of fields etc. Emitting IL or using expressions is almost always faster than using vanilla reflection.

There are many libraries like fasterflect or fastmember solving those performance problems so why couldn't it be faster out of the box? Would be cool

[jkotas]

Some of the potential solutions are discussed in https://github.com/dotnet/corefx/issues/24390

[steveharter]

Closing as duplicates of existing perf-related issues including
#19484
#23716
#7560