https://github.com/shader-slang/slang
Revision f3d637ba4d90bc2e23db07f1a9df5a6be7533f08 authored by Tim Foley on 04 June 2020, 18:53:13 UTC, committed by GitHub on 04 June 2020, 18:53:13 UTC
* First steps toward inheritance for struct types This change adds the ability for a `struct` type to declare a base type that is another `struct`: ```hlsl struct Base { int baseMember; } struct Derived : Base { int derivedMember; } ``` The semantics of the feature are that code like the above desugars into code like: ```hlsl struct Base { int baseMember; } struct Derived { Base _base; int derivedMember; } ``` At points where a member from the base type is being projected out, or the value is being implicitly cast to the base type, the compiler transforms the code to reference the implicitly-generated `_base` member. That means code like this: ```hlsl void f(Base b); ... Derived d = ...; int x = d.baseMember; f(d); ``` gets transformed into a form like this: ```hlsl void f(Base b); ... Derived d = ...; int x = d._base.baseMember; f(d._base); ``` Note that as a result of this choice, the behavior when passing a `Derived` value to a function that expects a `Base` (including to inherited member functions) is that of "object shearing" from the C++ world: the called function can only "see" the `Base` part of the argument, and any operations performed on it will behave as if the value was indeed a `Base`. There is no polymorphism going on because Slang doesn't currently have `virtual` methods. In an attempt to work toward inheritance being a robust feature, this change adds a bunch of more detailed logic for checking the bases of various declarations: * An `interface` declaration is only allowed to inherit from other `interface`s * An `extension` declaration can only introduce inheritance from `interface`s * A `struct` declaration can only inherit from at most one other `struct`, and that `struct` must be the first entry in the list of bases This change also adds a mechanism to control whether a `struct` or `interface` in one module can inherit from a `struct` or `interface` declared in another module: * If the base declaration is marked `[open]`, then the inheritance is allowed * If the base declaration is marked `[sealed]`, then the inheritance is allowed * If it is not marked otherwise, a `struct` is implicitly `[sealed]` * If it is not marked otherwise, an `interface` is implicitly `[open]` These seem like reasonable defaults. In order to safeguard the standard library a bit, the interfaces for builtin types have been marked `[sealed]` to make sure that a user cannot declare a `struct` and then mark it as a `BuiltinFloatingPointType`. This step should bring us a bit closer to being able to document and expose these interfaces for built-in types so that users can write code that is generic over them. There are some big caveats with this work, such that it really only represents a stepping-stone toward a usable inheritance feature. The most important caveats are: * If a `Derived` type tries to conform to an interface, such that one or more interface requirements are satisfied with members inherited from the `Base` type, that is likely to cause a crash or incorrect code generation. * If a `Derived` type tries to inherit from a `Base` type that conforms to one or more interfaces, the witness table generated for the conformance of `Derived` to that interface is likely to lead to a crash or incorrect code generation. It is clear that solving both of those issues will be necessary before we can really promote `struct` inheritance as a feature for users to try out. * fixup: trying to appease clang error * fixups: review feedback
1 parent 1b8731c
Tip revision: f3d637ba4d90bc2e23db07f1a9df5a6be7533f08 authored by Tim Foley on 04 June 2020, 18:53:13 UTC
First steps toward inheritance for struct types (#1366)
First steps toward inheritance for struct types (#1366)
Tip revision: f3d637b
File | Mode | Size |
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docs | ||
examples | ||
external | ||
prelude | ||
source | ||
tests | ||
tools | ||
.editorconfig | -rw-r--r-- | 937 bytes |
.gitattributes | -rw-r--r-- | 95 bytes |
.gitignore | -rw-r--r-- | 480 bytes |
.gitmodules | -rw-r--r-- | 774 bytes |
.travis.yml | -rw-r--r-- | 1.7 KB |
CODE_OF_CONDUCT.md | -rw-r--r-- | 3.1 KB |
LICENSE | -rw-r--r-- | 1.1 KB |
README.md | -rw-r--r-- | 7.4 KB |
appveyor.yml | -rw-r--r-- | 4.0 KB |
premake5.lua | -rw-r--r-- | 34.8 KB |
slang-com-helper.h | -rw-r--r-- | 4.8 KB |
slang-com-ptr.h | -rw-r--r-- | 4.8 KB |
slang-tag-version.h | -rw-r--r-- | 36 bytes |
slang.h | -rw-r--r-- | 128.0 KB |
slang.sln | -rw-r--r-- | 11.7 KB |
test.bat | -rw-r--r-- | 1.4 KB |
travis_build.sh | -rw-r--r-- | 460 bytes |
travis_test.sh | -rw-r--r-- | 435 bytes |
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