Question

I get a warning with the following code using ruby 1.9.3-p194

if (x = true)
  puts 'it worked'
end

# => warning: found = in conditional, should be ==

However, if I assign an array, no warning

if (x = [true])
  puts 'it worked'
end

# => 'it worked', then returns nil since return of 'puts' is nil

Why does using a string cause a warning? Or maybe a better question, why is it that using an array does NOT cause a warning?

Answer 1

Ruby reports warning when assigning (Literals: Fixnum, Symbol, String), nil and true/false

ruby-1.9.3-p194

parse.c:15026

static int
assign_in_cond(struct parser_params *parser, NODE *node)
{
    switch (nd_type(node)) {
      case NODE_MASGN:
        yyerror("multiple assignment in conditional");
        return 1;

      case NODE_LASGN:
      case NODE_DASGN:
      case NODE_DASGN_CURR:
      case NODE_GASGN:
      case NODE_IASGN:
        break;

      default:
        return 0;
    }

    if (!node->nd_value) return 1;
    switch (nd_type(node->nd_value)) {
      case NODE_LIT:
      case NODE_STR:
      case NODE_NIL:
      case NODE_TRUE:
      case NODE_FALSE:
        /* reports always */
        parser_warn(node->nd_value, "found = in conditional, should be ==");
        return 1;

      case NODE_DSTR:
      case NODE_XSTR:
      case NODE_DXSTR:
      case NODE_EVSTR:
      case NODE_DREGX:
      default:
        break;
    }
    return 1;
}