Add explicit to some constructors

paddle/operators/recurrent_op.h

@@ -19,8 +19,6 @@
 namespace paddle {
 namespace operators {
 
-using namespace paddle::framework;  // NOLINT
-
 namespace rnn {
 
 /**

paddle/platform/device_context.h

@@ -55,7 +55,7 @@ class CPUDeviceContext : public DeviceContext {
 
 class CUDADeviceContext : public DeviceContext {
  public:
-  CUDADeviceContext(GPUPlace);  // NOLINT
+  explicit CUDADeviceContext(GPUPlace);
   virtual ~CUDADeviceContext();
 
   /*! \brief  Wait for all operations completion in the stream. */

paddle/platform/place.h

@@ -32,7 +32,7 @@ struct CPUPlace {
 
 struct GPUPlace {
   GPUPlace() : GPUPlace(0) {}
-  GPUPlace(int d) : device(d) {}  // NOLINT
+  explicit GPUPlace(int d) : device(d) {}
 
   // needed for variant equality comparison
   inline bool operator==(const GPUPlace &o) const { return device == o.device; }

paddle/string/piece.h

@@ -39,8 +39,8 @@ public:
   // size_ is 0.
   Piece();
   Piece(const char* d, size_t n);
-  Piece(const char* d);         // NOLINT
-  Piece(const std::string& s);  // NOLINT
+  explicit Piece(const char* d);
+  explicit Piece(const std::string& s);
 
   const char* data() const { return data_; }
   size_t len() const { return size_; }