feat(Drop): liquid_method_missing and to_s

close #97

src/scope.js

@@ -60,16 +60,10 @@ const Scope = {
     if (_.isNil(obj)) {
       val = undefined
     } else {
-      if (typeof obj.to_liquid === 'function') {
-        obj = obj.to_liquid()
-      } else if (typeof obj.toLiquid === 'function') {
-        obj = obj.toLiquid()
-      }
-
-      if (key === 'size' && (_.isArray(obj) || _.isString(obj))) {
-        val = obj.length
-      } else {
-        val = obj[key]
+      obj = toLiquid(obj)
+      val = key === 'size' ? readSize(obj) : obj[key]
+      if (_.isFunction(obj.liquid_method_missing)) {
+        val = obj.liquid_method_missing(key)
       }
     }
     if (_.isNil(val) && this.opts.strict_variables) {
@@ -138,6 +132,22 @@ const Scope = {
   }
 }
 
+function toLiquid (obj) {
+  if (_.isFunction(obj.to_liquid)) {
+    return obj.to_liquid()
+  }
+  if (_.isFunction(obj.toLiquid)) {
+    return obj.toLiquid()
+  }
+  return obj
+}
+
+function readSize (obj) {
+  if (!_.isNil(obj.size)) return obj.size
+  if (_.isArray(obj) || _.isString(obj)) return obj.length
+  return obj.size
+}
+
 function matchRightBracket (str, begin) {
   let stack = 1 // count of '[' - count of ']'
   for (let i = begin; i < str.length; i++) {

src/util/underscore.js

@@ -1,4 +1,5 @@
 const toStr = Object.prototype.toString
+const arrToStr = Array.prototype.toString
 
 /*
  * Checks if value is classified as a String primitive or object.
@@ -9,6 +10,10 @@ export function isString (value) {
   return toStr.call(value) === '[object String]'
 }
 
+export function isFunction (value) {
+  return typeof value === 'function'
+}
+
 export function promisify (fn) {
   return function () {
     return new Promise((resolve, reject) => {
@@ -20,19 +25,16 @@ export function promisify (fn) {
 }
 
 export function stringify (value) {
-  if (isNil(value)) {
-    return String(value)
-  }
-  if (typeof value.to_liquid === 'function') {
-    return stringify(value.to_liquid())
-  }
-  if (typeof value.toLiquid === 'function') {
-    return stringify(value.toLiquid())
-  }
-  if (isString(value) || value instanceof RegExp || value instanceof Date) {
-    return value.toString()
-  }
+  if (isNil(value)) return String(value)
+  if (isFunction(value.to_liquid)) return stringify(value.to_liquid())
+  if (isFunction(value.toLiquid)) return stringify(value.toLiquid())
+  if (isFunction(value.to_s)) return value.to_s()
+  if ([toStr, arrToStr].indexOf(value.toString) > -1) return defaultToString(value)
+  if (isFunction(value.toString)) return value.toString()
+  return toStr.call(value)
+}
 
+function defaultToString (value) {
   const cache = []
   return JSON.stringify(value, (key, value) => {
     if (isObject(value)) {