Method sets.. Some confusion aroudn type T values calling methods with receivers of type *T

Getting Help
#1

https://play.golang.org/p/EtGkpo3Wav-

Question here is on line 21 f.bar() why does it work. If I were to go with the spec

  • The method set of any other type T consists of all [methods] declared with receiver type T
  • The method set of the corresponding [pointer type] *T is the set of all methods declared with receiver *T or T (that is, it also contains the method set of T ).

Then since f is of type T and bar is a receiver method of type *T I would have imagined I would have gotten a compile error. But I didn’t. Seems like the compiler stuck in & behind the scenes and it all worked ! Why will it do that? If it does that there then why doesn’t it do it in line 38, w.bar() and hence not give a compile error? Also seems when the compiler is figuring out the types interface implementation it is going by the spec definition. But when we are calling the method via a value it is doing an extra step. Seems not consistent between the two…I am sure good reason but cant fully understand the reason…

#2

The differences in behavior that you’re seeing are the differences/interactions between concrete and interface types (concrete types being everything other than interfaces).

The compiler can implicitly take the address of a concrete type T to get a *T, so you’re right about line 21 being automatically compiled as (&f).foo()

The compiler does not, however, implicitly take the address of a value when “boxing” the value into an interface value. There you have to be explicit.

I don’t know the reason for this, but I suspect the language designers didn’t see any ambiguity calling pointer method receiver functions on values but didn’t want implicit conversions to interface types. You could write info(&f) and I think that should work.

#3

Hi, I recently stumbled upon the same difference in bahaviors and just compiled some relatively detailed summary with a bit of speculation in the end. Analogies to C/C++ included.

The post contains more than asked onthe question, and that’s on purpose to compile some context around the topic. Feedback welcome!

#4

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