增加api

Author: Eric Wu

CRBoostSwift/Classes/CRMath.swift

@@ -420,6 +420,16 @@ public func CRUUIDString() -> String {
     return NSUUID().uuidString
 }
 
+// MARK: - timer
+
+public func CRStopTimer(_ tmr: Timer?) {
+    if let timer = tmr {
+        if timer.isValid {
+            timer.invalidate()
+        }
+    }
+}
+
 // MARK: - GCD
 
 public func CRRunOnMainThread(task: @escaping CRVoidBlock) {

CRBoostSwift/Classes/Foundation+CRBoost.swift

@@ -124,6 +124,26 @@ extension String {
         return result
     }
 
+    @discardableResult
+    public func safeRemoveFirst(_ k: Int = 1) -> String {
+        if count < k {
+            return self
+        }
+        var result = self
+        result.removeFirst(k)
+        return result
+    }
+
+    @discardableResult
+    public func safeRemoveLast(_ k: Int = 1) -> String {
+        if count < k {
+            return self
+        }
+        var result = self
+        result.removeLast(k)
+        return result
+    }
+
     @discardableResult
     public func retainDecimal(_ digits: Int) -> String {
         let formatter = NumberFormatter()