You have to define the struct for sure, but beyond that you just pass it to binary.Read and it comes back with the fields populated. I don’t see how you’d avoid defining the struct.
https://github.com/danos/vyatta-dataplane/blob/master/src/ecmp.c#L108-L116
Once one has to handle that sort of situation, and actually copy the data, the lack of language support for such type-punning becomes immaterial.
If the misaligned access is slow… it will be slow whether the compiler reads the variable or if you hand-write even slower and error prone code.
That said, please show me a protocol that generates unaligned accesses on any architecture. People writing protocols aren't noobs :)
func Foo(r io.Reader) {
var m MyStruct
binary.Read(r, binary.LittleEndian, &m)
}