This distinction was useful before when reflect wasn't properly
supported. Back then it made sense to only include method sets that were
actually used in an interface. But now that it is possible to get to
other values (for example, by extracting fields from structs) and it is
possible to turn them back into interfaces, it is necessary to preserve
all method sets that can possibly be used in the program in a type
assert, interface assert or interface method call.
In the future, this logic will need to be revisited again when
reflect.New or reflect.Zero gets implemented.
Code size increases a bit in some cases, but usually in a very limited
way (except for one outlier in the drivers smoke tests). The next commit
will improve the situation significantly.
When using reflect, arbitrary types can be synthesized. This invalidates
a few assumptions in the interface-lowering pass, that think they can
see all types that are in use in a program and optimize accordingly.
The file size impact depends on the specific program. Sometimes it's
nonexistent, sometimes it's rather hefty (up to 30% bigger). Especially
the samd21 targets seem to be affected, with a 2000-6000 bytes increase
in code size. A moderately large case (the stdlib test) increases by
4%/6%/15% depending on the target.
I hope that this increase could be mitigated, but I don't see an obvious
way to do that.
Linked lists are usually implemented as follows:
type linkedList struct {
next *linkedList
data int // whatever
}
This caused a stack overflow while writing out the reflect run-time type
information. This has now been fixed by splitting the allocation of a
named type number from setting the underlying type in the sidetable.
With this change, it becomes possible to get the element type of named
slices, pointers, and channels.
This is a prerequisite to enable the common named struct types. There's
more to come.
This commit makes sure all Go types can be encoded in the interface type
code, so that Type.Kind() always returns a proper type kind for any
non-nil interface.
Ayke van Laethem
Cornel