Make Type hierarchy methods const

[edi33416]

This PR is useful to the the C++ header generator to generate the dmd frontend header files that are used by gdc.

For a detailed description of the motivation, please see PR

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[edi33416]

CC @rainers @andralex @jacob-carlborg

[rainers]

The number of necessary cast() operations is a bit worrying. Maybe this can be mitigated by declaring methods like nextOf, memType and elementType inout?

[jacob-carlborg]

I suggest you start with the leaf functions to avoid the need for cast() all over the place. Unfortunately it seems that DMD modifies the internal state of AST nodes in a lot of the getXXX and isXXX methods.

[ibuclaw]

You should update Target::alignsize as receiving a const parameter to avoid unnecessary cast.

[ibuclaw]

Why is this necessary? You're not making modifications here.

[edi33416]

The number of necessary cast() operations is a bit worrying.

I agree. Especially since, as @jacob-carlborg pointed out:

Unfortunately it seems that DMD modifies the internal state of AST nodes in a lot of the getXXX and isXXX methods.

Maybe this can be mitigated by declaring methods like nextOf, memType and elementType inout?

I'll give inout a try. I attempted to make them const and that just blew up in my face.

[jacob-carlborg]

inout will not help with the get and is methods. An inout will behave inside the method as a const method.

const in D does not support logical const. It’s been mentioned thousands of times.

[jacob-carlborg]

You can try my tool DLP to identify leaf functions. https://github.com/jacob-carlborg/dlp

[edi33416]

I think that because the get and is methods lazily initialise internal state, properly adding const throughout the code base will require a lot of non trivial changes. I propose that we delete the const qualifier from the few methods that have one, in the Type hierarchy.