disassemble-some-codes.md

Disassemble Some Codes

The RubyVM::InstructionSequence class makes it easy to compile, disassemble, and inspect bits of Ruby code. We can quickly take a peek under the hood at a simple ruby statement, such as a = 1 + 2, like so:

> ruby_code = 'a = 1 + 2'
=> a = 1 + 2
> compiled_code = RubyVM::InstructionSequence.compile(ruby_code)
=> <RubyVM::InstructionSequence:<compiled>@<compiled>>
> puts compiled_code.disasm
== disasm: <RubyVM::InstructionSequence:<compiled>@<compiled>>==========
local table (size: 2, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw:
-1@-1, kwrest: -1])
[ 2] a
0000 trace            1                                               (   1)
0002 putobject_OP_INT2FIX_O_1_C_
0003 putobject        2
0005 opt_plus         <callinfo!mid:+, argc:1, ARGS_SIMPLE>
0007 dup
0008 setlocal_OP__WC__0 2
0010 leave
=> nil

It is a bit archaic, but when we get to the line starting with 0002, we see values (1 and then 2) pushed onto the stack, then operated on, and finally set on the local variable a. Fun!