THRIFT-2232 IsSet* broken in Go

Patch: Ben Sigelman

2 files changed, 85 insertions, 2 deletions

diff --git a/lib/go/README b/lib/go/README
index 94628d9de..87ba6f903 100644
--- a/lib/go/README
+++ b/lib/go/README
@@ -1,4 +1,4 @@
-Thrift Python Software Library
+Thrift Go Software Library
 
 License
 =======
@@ -20,12 +20,47 @@ KIND, either express or implied. See the License for the
 specific language governing permissions and limitations
 under the License.
 
+
 Using Thrift with Go
 ====================
 
 In following Go conventions, we reccomend you use the 'go' tool to install
 Thrift for go.
 
-$ go get git.apache.org/thrift.git/lib/go/thrift
+    $ go get git.apache.org/thrift.git/lib/go/thrift
 
 Will install the last stable release.
+
+
+A note about optional fields
+============================
+
+The thrift-to-Go compiler tries to represent thrift IDL structs as Go structs.
+We must be able to distinguish between optional fields that are set to their
+default value and optional values which are actually unset, so the generated
+code represents optional fields via pointers.
+
+This is generally intuitive and works well much of the time, but Go does not
+have a syntax for creating a pointer to a constant in a single expression. That
+is, given a struct like
+
+    struct SomeIDLType {
+    	OptionalField *int32
+    }
+
+, the following will not compile:
+
+    x := &SomeIDLType{
+    	OptionalField: &(3),
+    }
+
+(Nor is there any other syntax that's built in to the language)
+
+As such, we provide some helpers that do just this under lib/go/thrift/. E.g.,
+
+    x := &SomeIDLType{
+    	OptionalField: thrift.Int32Ptr(3),
+    }
+
+And so on. The code generator also creates analogous helpers for user-defined
+typedefs and enums.
diff --git a/lib/go/thrift/pointerize.go b/lib/go/thrift/pointerize.go
new file mode 100644
index 000000000..c2ae26102
--- /dev/null
+++ b/lib/go/thrift/pointerize.go
@@ -0,0 +1,48 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package thrift
+
+///////////////////////////////////////////////////////////////////////////////
+// This file is home to helpers that convert from various base types to
+// respective pointer types. This is necessary because Go does not permit
+// references to constants, nor can a pointer type to base type be allocated
+// and initialized in a single expression.
+//
+// E.g., this is not allowed:
+//
+//    var ip *int = &5
+//
+// But this *is* allowed:
+//
+//    func IntPtr(i int) *int { return &i }
+//    var ip *int = IntPtr(5)
+//
+// Since pointers to base types are commonplace as [optional] fields in
+// exported thrift structs, we factor such helpers here.
+///////////////////////////////////////////////////////////////////////////////
+
+func Float32Ptr(v float32) *float32 { return &v }
+func Float64Ptr(v float64) *float64 { return &v }
+func IntPtr(v int) *int             { return &v }
+func Int32Ptr(v int32) *int32       { return &v }
+func Int64Ptr(v int64) *int64       { return &v }
+func StringPtr(v string) *string    { return &v }
+func Uint32Ptr(v uint32) *uint32    { return &v }
+func Uint64Ptr(v uint64) *uint64    { return &v }