vault backup: 2024-10-12 17:19:45

03-UnrealEngine/Gameplay/UObject/UnrealSpecifiers/Meta/Script/ScriptConstant.md

@@ -0,0 +1,113 @@
+# ScriptConstant
+
+- **功能描述：** 把一个静态函数的返回值包装成为一个常量值。
+- **使用位置：** UFUNCTION
+- **引擎模块：** Script
+- **元数据类型：** string="abc"
+- **关联项：** [ScriptConstantHost](ScriptConstantHost.md)
+- **常用程度：** ★★★
+
+把一个静态函数的返回值包装成为一个常量值。
+
+- 函数的名字即为常量的默认名称，但ScriptConstant也可以额外提供一个自定义名称。
+- 常量作用域默认存在于该静态函数的外部类中，但也可以通过ScriptConstantHost来指定到另外一个类型中。
+
+## 测试代码：
+
+```cpp
+USTRUCT(BlueprintType)
+struct INSIDER_API FMyPythonConstantStruct
+{
+	GENERATED_BODY()
+public:
+	UPROPERTY(BlueprintReadWrite, EditAnywhere)
+	FString MyString;
+};
+
+UCLASS(Blueprintable, BlueprintType)
+class INSIDER_API UMyPython_ConstantOwner :public UObject
+{
+	GENERATED_BODY()
+public:
+};
+
+UCLASS(Blueprintable, BlueprintType)
+class INSIDER_API UMyPython_Constant_Test :public UObject
+{
+	GENERATED_BODY()
+public:
+	UFUNCTION(BlueprintPure, meta = (ScriptConstant))
+	static int32 MyIntConst() { return 123; }
+
+	UFUNCTION(BlueprintPure, meta = (ScriptConstant = "MyOtherIntConst"))
+	static int32 MyIntConst2() { return 456; }
+
+	UFUNCTION(BlueprintPure, meta = (ScriptConstant))
+	static FMyPythonConstantStruct MyStructConst() { return FMyPythonConstantStruct{ TEXT("Hello") }; }
+
+	UFUNCTION(BlueprintPure, meta = (ScriptConstant = "MyOtherStructConst"))
+	static FMyPythonConstantStruct MyStructConst2() { return FMyPythonConstantStruct{ TEXT("World") }; }
+
+public:
+	UFUNCTION(BlueprintPure, meta = (ScriptConstant="FirstString", ScriptConstantHost = "/Script/Insider.MyPython_ConstantOwner"))
+	static FString MyStringConst() { return TEXT("First"); }
+****};
+
+```
+
+## 生成的Py代码：
+
+```cpp
+class MyPython_Constant_Test(Object):
+    r"""
+    My Python Constant Test
+    
+    **C++ Source:**
+    
+    - **Module**: Insider
+    - **File**: MyPython_ScriptConstant.h
+    
+    """
+    MY_OTHER_STRUCT_CONST: MyPythonConstantStruct #: (MyPythonConstantStruct): My Struct Const 2
+    MY_STRUCT_CONST: MyPythonConstantStruct #: (MyPythonConstantStruct): My Struct Const
+    MY_OTHER_INT_CONST: int #: (int32): My Int Const 2
+    MY_INT_CONST: int #: (int32): My Int Const
+    
+class MyPython_ConstantOwner(Object):
+    r"""
+    **My Python Constant Owner
+    
+    **C++ Source:**
+    
+    - **Module**: Insider
+    - **File**: MyPython_ScriptConstant.h
+    
+    """
+    FIRST_STRING: str #: (str): My String Const
+```
+
+## 运行的结果：
+
+可见在类中生成了相应的常量。而MyStringConst因为指定了ScriptConstantHost 而生成在别的类中。
+
+```cpp
+LogPython: print(unreal.MyPython_Constant_Test.MY_INT_CONST)
+LogPython: 123
+LogPython: print(unreal.MyPython_Constant_Test.MY_OTHER_INT_CONST)
+LogPython: 456
+LogPython: print(unreal.MyPython_Constant_Test.MY_OTHER_STRUCT_CONST)
+LogPython: <Struct 'MyPythonConstantStruct' (0x00000A0FC4051F00) {my_string: "World"}>
+LogPython: print(unreal.MyPython_Constant_Test.MY_STRUCT_CONST)
+LogPython: <Struct 'MyPythonConstantStruct' (0x00000A0FC4051EA0) {my_string: "Hello"}>
+LogPython: print(unreal.MyPython_ConstantOwner.FIRST_STRING)
+LogPython: First
+```
+
+## 原理：
+
+生成的逻辑在这个GenerateWrappedConstant 函数里。
+
+```cpp
+auto GenerateWrappedConstant = [this, &GeneratedWrappedType, &OutGeneratedWrappedTypeReferences, &OutDirtyModules](const UFunction* InFunc)
+{}
+```