src/compile/references.js
function(property, baseRef) {
      var ast = property.id;
      var key;
      if (ast.type === 'references') {
        key = this.getReferences(ast);
      } else if (ast.type === 'integer') {
        key = ast.value;
      } else {
        key = ast.value;
      }

      return baseRef[key];
    }
function(property, baseRef) {
      var ast = property.id;
      var key;
      if (ast.type === 'references') {
        key = this.getReferences(ast);
      } else if (ast.type === 'integer') {
        key = ast.value;
      } else {
        key = ast.value;
      }

      return baseRef[key];
    }
$foo.bar[1] index求值
@private