1 files changed, 8 insertions, 7 deletions
diff --git a/lib/plum/frame_factory.rb b/lib/plum/frame_factory.rb
index 686f88e..51908ec 100644
--- a/lib/plum/frame_factory.rb
+++ b/lib/plum/frame_factory.rb
@@ -1,3 +1,4 @@
+# -*- frozen-string-literal: true -*-
 using Plum::BinaryString
 
 module Plum
@@ -6,7 +7,7 @@ module Plum
     # @param stream_id [Integer] The stream ID.
     # @param error_type [Symbol] The error type defined in RFC 7540 Section 7.
     def rst_stream(stream_id, error_type)
-      payload = "".push_uint32(HTTPError::ERROR_CODES[error_type])
+      payload = String.new.push_uint32(HTTPError::ERROR_CODES[error_type])
       Frame.new(type: :rst_stream, stream_id: stream_id, payload: payload)
     end
 
@@ -16,9 +17,9 @@ module Plum
     # @param message [String] Additional debug data.
     # @see RFC 7540 Section 6.8
     def goaway(last_id, error_type, message = "")
-      payload = "".push_uint32((last_id || 0) | (0 << 31))
-                  .push_uint32(HTTPError::ERROR_CODES[error_type])
-                  .push(message)
+      payload = String.new.push_uint32((last_id || 0) | (0 << 31))
+                          .push_uint32(HTTPError::ERROR_CODES[error_type])
+                          .push(message)
       Frame.new(type: :goaway, stream_id: 0, payload: payload)
     end
 
@@ -26,7 +27,7 @@ module Plum
     # @param ack [Symbol] Pass :ack to create an ACK frame.
     # @param args [Hash<Symbol, Integer>] The settings values to send.
     def settings(ack = nil, **args)
-      payload = args.inject("") {|payload, (key, value)|
+      payload = args.inject(String.new) {|payload, (key, value)|
         id = Frame::SETTINGS_TYPE[key] or raise ArgumentError.new("invalid settings type")
         payload.push_uint16(id)
         payload.push_uint32(value)
@@ -71,8 +72,8 @@ module Plum
     # @param encoded [String] Request headers.
     # @param flags [Array<Symbol>] Flags.
     def push_promise(stream_id, new_id, encoded, *flags)
-      payload = "".push_uint32(0 << 31 | new_id)
-                  .push(encoded)
+      payload = String.new.push_uint32(new_id)
+                          .push(encoded)
       Frame.new(type: :push_promise, stream_id: stream_id, flags: flags, payload: payload)
     end