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[spec/struct] Add Member Functions section #4235

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[spec/struct] Add Member Functions section #4235

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37 changes: 35 additions & 2 deletions spec/struct.dd
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Original file line number Diff line number Diff line change
Expand Up @@ -104,9 +104,9 @@ $(H3 $(LNAME2 struct-members, Struct Members))
$(LI Fields)
$(LI $(DDSUBLINK spec/attribute, static, Static) fields)
$(LI $(RELATIVE_LINK2 anonymous, Anonymous Structs and Unions))
$(LI $(DDSUBLINK spec/class, member-functions, member functions)
$(LI $(RELATIVE_LINK2 member-functions, Member Functions)
$(UL
$(LI static member functions)
$(LI $(DDSUBLINK spec/attribute, static, Static) member functions)
$(LI $(RELATIVE_LINK2 struct-constructor, Constructors))
$(LI $(RELATIVE_LINK2 struct-destructor, Destructors))
$(LI $(RELATIVE_LINK2 Invariant, Invariants))
Expand Down Expand Up @@ -2127,6 +2127,39 @@ void main()
---
)


$(H2 $(LNAME2 member-functions, Member Functions (a.k.a. Methods)))

$(P A struct/union can have non-static member functions,
$(DDSUBLINK spec/class, member-functions, like classes).
Such functions (called instance methods) have a hidden
$(DDSUBLINK spec/expression, this, `this` parameter) which is a reference
to the struct instance.
However, an instance method can still be called on an rvalue struct instance,
even if the method is not const:)

$(SPEC_RUNNABLE_EXAMPLE_COMPILE
---
struct S
{
int i;
int f() => ++i;
}

void main()
{
//S().i++; // cannot modify, `S().i` is not an lvalue
assert(S().f() == 1); // OK
}
---
)

$(RATIONALE An instance method may have other side effects besides mutating a field,
or it may produce a useful return value. In the general case, throwing
away changes to a field after the method returns does not necessarily indicate
a logic error.)


$(H2 $(LEGACY_LNAME2 StructDestructor, struct-destructor, Struct Destructors))

$(P Destructors are called implicitly when an object goes out of scope, or
Expand Down