I have go versions 1.13.1 and 1.12.9 installed
$brew list --versions | grep go
go 1.13.1
go@1.12 1.12.9
But I am unable to switch to 1.12, an error indicates that I only have version 1.13.1 installed contradicting the earlier listing.
$brew switch go 1.12
Error: go does not have a version "1.12" in the Cellar.
go installed versions: 1.13.1
And when I look carefully at go versions (no grep)
$brew list --versions go
go 1.13.1
So I must have done something wrong when I installed go 1.12, but what? I used brew install go@1.12, should I have used another syntax?