feat: Polymorphism #1493
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feat: Polymorphism #1493
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`POINTER TO <function>` are now indexed in the codegen
…for less nosiy output
Previously when dealing with function pointer calls such as `fnPtr^()`
the resolver would only annotate the operator and any arguments. Some
codegen parts require an annotation on the whole call statement however
(which makes sense), as such this commit fixes the described issue.
Visuallized, assuming `fnPtr` points to a function returning a DINT:
```
fnPtr^();
^^^^^^^^ -> StatementAnnotation::Value { resulting_type: "DINT" }
```
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Function pointers can now point to the body of a function block, allowing
for code execution such as
```
FUNCTION_BLOCK A
VAR
localState: DINT := 5;
END_VAR
METHOD foo
// ...
END_METHOD
printf('localState = %d$N', localState);
END_FUNCTION_BLOCK
FUNCTION main
VAR
instanceA: A;
fnBodyPtr: FNPTR A := ADR(A);
END_VAR
fnBodyPtr^(instanceA); // prints "localState = 5"
END_FUNCTION
```
Also inject `__vtable` member variable into "root" POUs
Methods calls which must make use of the virtual table are now
desugared. For example a method call within a method such as `foo(1, 2)`
will now be desugared into `__vtable_{FB_NAME}#(THIS^.__vtable^).foo^(THIS^, 1, 2)`.
Similarly, a variable like `refInstance: POINTER TO FbA` making a method call
such as `refInstance^.foo(1, 2)` will be lowered into some similar form, except
not making use of THIS, rather of the operator name (excluding the method name), i.e.
`__vtable_FbA#(refInstance^.__vtable^).foo(refInstance^, 1, 2)`.
The `__vtable` member field is now initialized with a right hand side of `ADR(__vtable_<POU_NAME>_instance)` which represents the global instance variable of a virtual table that is initialized with its function pointers.
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The `__body` function pointer now points at the function blocks body
method in the virtual table struct. As a result, code execution like
the following is now possible
```
VAR
instanceA: A;
instanceB: B; // Child of A
refInstanceA: POINTER TO A;
END_VAR
refInstanceA := ADR(A);
refInstanceA^(); // Calls body method of A
refInstanceA := ADR(B);
refInstanceA^(); // Calls body method of B
```
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