decompile .NET Replace method (v4.6.1)

Question

I want to see how the

public String Replace(String oldValue, String newValue);

method that is inside mscorlib.dll (System.String) works.

I decompiled the mscorlib.dll with dotPeek and inside the method there is a call to ReplaceInternal method which I cannot find it

string s = ReplaceInternal(oldValue, newValue);

I have search for this method even on the open source .NET Core from GIT but no luck.

Please explain where is this method and what is inside?

Answer 1

The extern C++ code is here.

https://github.com/gbarnett/shared-source-cli-2.0/blob/master/clr/src/vm/comstring.cpp

Line 1578 has

FCIMPL3(Object*, COMString::ReplaceString, StringObject* thisRefUNSAFE, StringObject* oldValueUNSAFE, StringObject* newValueUNSAFE)

Answer 2

Having a look here, you will notice this:

// This method contains the same functionality as StringBuilder Replace. 
// The only difference is that
// a new String has to be allocated since Strings are immutable
[System.Security.SecuritySafeCritical]  // auto-generated
[ResourceExposure(ResourceScope.None)]
[MethodImplAttribute(MethodImplOptions.InternalCall)]
private extern String ReplaceInternal(String oldValue, String newValue);

The extern keyword means that this method is implemented externally, in another dll.

That being said, it may be even written in a not managed dll (in C++ quite possibly), that is used by this module. So you can't decompile this code or see it, as you usually do with managed code.

Update

After a little searching I found the corresponding code in the coreclr project:

https://github.com/dotnet/coreclr/blob/master/src/classlibnative/bcltype/stringnative.cpp