接口字段记录 [英] Interface field in record
问题描述
nil ？ TMyRec = record
FGuard：IInterface;
FObject：TObject;
程序CheckCreated;
结束
这将允许我写：
程序TMyCheck.CheckCreated;
begin
if（FGuard = nil）then
begin
FObject：= TObject.Create;
FGuard：= TGuard.Create（FObject）;
结束
结束
（用于自动终身管理）
我知道接口字段被初始化为 nil ，但是当包含在记录中时也是如此？
所有引用计数的变量：
- 字符串;
- 动态数组;
- 变体;
- 包含这些变量的嵌套记录。
初始化为记录时，甚至在本地堆叠。当然，如果你使用一个简单的 GetMem 或使用指针，你必须自己初始化它（例如使用一个 FillChar ）。
如果您好奇，则会对System.pas的以下过程隐藏调用：
procedure _InitializeRecord（p：Pointer; typeInfo：Pointer）;
这将把所有引用计数的变量内存填充为0，但不会设置其他成员的记录。实际上，在一个类实例中，整个字段内存被初始化为0，包括所有成员 - 记录 ，初始化仅用于引用计数的类型。
请注意，在某些情况下，我发现如果使用对象类型而不是记录 - 至少在Delphi 2009-2010中。所以如果你的代码有一些对象类型声明，你最好切换到记录（和松散继承）调用 FillChar 。
如果你好奇，这里是我在asm中写的一个优化版本 - 可在我们的增强型RTL 。
procedure _InitializeRecord（p：Pointer; typeInfo：Pointer）;
//这个过程在大多数对象创建中被调用 - >优化岩石在这里！
asm
{ - > EAX指针，以记录初始化}
{EDX指针类型信息}
MOVZX ECX，[EDX + 1] {类型名称长度}
PUSH EBX
PUSH ESI
PUSH EDI
MOV EBX，EAX // PIC安全。见上面的评论
LEA ESI，[EDX + ECX + 2 + 8] {可破坏领域的地址}
MOV EDI，[EDX + ECX + 2 + 4] {可破坏领域的数量}
@@ loop：
mov edx，[esi] //键入info
mov eax，[esi + 4]
mov edx，[edx]
add esi，8
添加eax，ebx //要初始化的数据
movzx ecx，[edx] //数据类型
cmp ecx，tkLString
je @@ LString
jb @@ err
cmp ecx，tkDynArray
je @@ DynArray
ja @@ err
jmp dword ptr [ecx * 4 + @@ Tab-tkWString * 4]
nop ; nop nop // align @@ Tab
@@ Tab：dd @@ WString，@@ Variant，@@ Array，@@ Record
dd @@ Interface，@@ err
@@ LString ：
@@ WString：
@@接口：
@@ DynArray：// EAX
中的零4个字节b dec edi
mov dword ptr [eax]，0
jg @@ loop
POP EDI
POP ESI
POP EBX
RET
@@变式：//零EAX $ 16 $ b中的16个字节ecx
dec edi
mov [eax]，ecx
mov [eax + 4]，ecx
mov [eax + 8]，ecx
mov [ eax + 12]，ecx
jg @@ loop
jmp @@ exit
@@ err：
MOV AL，reInvalidPtr
POP EDI
POP ESI
POP EBX
JMP错误
@@数组：
@@记录：//在实践中很少调用
mov ecx，1
调用_InitializeArray
dec edi
jg @@ loop
@@ exit：
POP EDI
POP ESI
POP EBX
结束;
Can I rely on the fact, that an interface field in a record is always initialized to nil?
TMyRec = record
FGuard : IInterface;
FObject : TObject;
procedure CheckCreated;
end;
This would allow me to write:
procedure TMyCheck.CheckCreated;
begin
if (FGuard = nil) then
begin
FObject := TObject.Create;
FGuard := TGuard.Create (FObject);
end;
end;
(for automatic lifetime management)
I know that interface fields are initialized to nil but is that also true when contained in a record?
Yes you can rely on that.
All reference-counted variables:
- Strings;
- Dynamic arrays;
- Variants;
- Interfaces;
- Nested records containing those kind of variables.
are initialized to nil when a record is allocated, if you use New or a dynamic array - even locally on the stack. Of course, if you use a plain GetMem or work with pointers, you'll have to initialize it by yourself (e.g. using a FillChar).
If you are curious, there is an hidden call to the following procedure of System.pas:
procedure _InitializeRecord(p: Pointer; typeInfo: Pointer);
This will fill all the reference-counted variables memory to 0, but won't set the other members of the record. In fact, in a class instance, the whole field memory is initialized with 0, including all members - for a record, the initialization is only for reference-counted types.
Note that in some cases, I've found out that this initialization was not properly generated if you use the object type instead of record - at least under Delphi 2009-2010. So if your code has some object type declaration, you may better switch to record (and loose inheritance), or explicitly call FillChar.
If you are curious, here is an optimized version I wrote in asm - available in our enhanced RTL.
procedure _InitializeRecord(p: Pointer; typeInfo: Pointer);
// this procedure is called at most object creation -> optimization rocks here!
asm
{ -> EAX pointer to record to be initialized }
{ EDX pointer to type info }
MOVZX ECX,[EDX+1] { type name length }
PUSH EBX
PUSH ESI
PUSH EDI
MOV EBX,EAX // PIC safe. See comment above
LEA ESI,[EDX+ECX+2+8] { address of destructable fields }
MOV EDI,[EDX+ECX+2+4] { number of destructable fields }
@@loop:
mov edx,[esi] // type info
mov eax,[esi+4]
mov edx,[edx]
add esi,8
add eax,ebx // data to be initialized
movzx ecx,[edx] // data type
cmp ecx,tkLString
je @@LString
jb @@err
cmp ecx,tkDynArray
je @@DynArray
ja @@err
jmp dword ptr [ecx*4+@@Tab-tkWString*4]
nop; nop; nop // align @@Tab
@@Tab: dd @@WString,@@Variant,@@Array,@@Record
dd @@Interface,@@err
@@LString:
@@WString:
@@Interface:
@@DynArray: // zero 4 bytes in EAX
dec edi
mov dword ptr [eax],0
jg @@loop
POP EDI
POP ESI
POP EBX
RET
@@Variant: // zero 16 bytes in EAX
xor ecx,ecx
dec edi
mov [eax],ecx
mov [eax+4],ecx
mov [eax+8],ecx
mov [eax+12],ecx
jg @@loop
jmp @@exit
@@err:
MOV AL,reInvalidPtr
POP EDI
POP ESI
POP EBX
JMP Error
@@Array:
@@Record: // rarely called in practice
mov ecx,1
call _InitializeArray
dec edi
jg @@loop
@@exit:
POP EDI
POP ESI
POP EBX
end;
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