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d05用用定属来自定义

IT知识自定义自定定义

少年辛苦终身事，莫向光阴惰寸功。这篇文章主要讲述d05用用定属来自定义相关的知识，希望能为你提供帮助。

?
??D??中??用定属??可以为??构/原始类型/编译时执行函数(返回值)??.
用??@TypeName??附加,用??__traits(getAttributes)??来取??用定属??.

enum AnEnum{a}
struct AStruct{}
class AClass{}

int FunctionThatReturnsTheUDAValue(){ return 0; }

@AnEnum
@AStruct
@AClass
@FunctionThatReturnsTheUDAValue
struct Test{}

void main()
{
import std.traits;
// __traits(getAttributes)返回符号上的所有`用定属`元组
static foreach(uda; __traits(getAttributes, Test))
pragma(msg, uda);

/*
输出:
AnEnum
AStruct
AClass
0
*/
}


还有??std.traits#hasUDA和std.traits#getUDAs??,来??有/取??用定属.??std.traits#getSymbolsByUDA??这个也很方便.

struct UsefulUDA
{
string some;
int data;
}

struct NeverUsedUDA
{
}

struct MultiUDA
{
string data;
}

@UsefulUDA("Foo", 21)
@MultiUDA("Use")
@MultiUDA("Me")
@(MultiUDA("Multiple"), MultiUDA("Times"))
struct MyStruct
{

}

void main()
{
import std.traits : hasUDA, getUDAs;
import std.stdio: writeln, write;

writeln("构有@UsefulUDA?: ", hasUDA!(MyStruct, UsefulUDA));
writeln("@NeverUsedUDA呢?:", hasUDA!(MyStruct, NeverUsedUDA));

// 可多次用UDAs,getUDAs返回所有.
const UsefulUDA useful = getUDAs!(MyStruct, UsefulUDA)[0]; //要用[0]取第1个.
writeln(useful);

// 多次遍历
static foreach(uda; getUDAs!(MyStruct, MultiUDA))
write(uda.data, " ");

/*
输出:
构有@UsefulUDA?: true
@NeverUsedUDA呢?:false
const(UsefulUDA)("Foo", 21)
Use Me Multiple Times
*/
}


我们用如下??三个??属性来更新??序化器??.
??属性??
意思
??@Ignore??
忽略字段
??@Name??
自定义名字
??@ByValue??
按值??序化??枚举,而非??名字??.
我们用??构??来表示??用定属??.

struct ByValue {}
struct Ignore {}

struct Name
{
string name;
}

// 保留`Person`,用它来比较`用定属`的输出
struct Person
{
string name;
int age;
PersonType type;
}

struct PersonWithUDAs
{//带用定属的人.
@Ignore
string name;

@Name("yearsOld")
int age;

@ByValue
PersonType type;
}


实现@忽略由于??静每一(a)??的??展开??.??a??与??下??的合作不是很好.因而,得有点技巧.我们把??静每一??锁在??检查是否忽略??字段的??静如??之后.如下在序化??构/类??的??{{}}??:

static foreach(member; T.tupleof)
{{
alias MemberType = typeof(member);
const MemberName = __traits(identifier, member);

MemberType memberValue = https://www.songbingjia.com/android/mixin("value." ~ MemberName);

//静每一,如果`没有`忽略字段.
static if(!hasUDA!(member, Ignore))
{
toReturn[MemberName] = serialise(memberValue);
}
}}


同样:??反序化??中这样:

static foreach(member; T.tupleof)
{{
alias MemberType = typeof(member);
const MemberName = __traits(identifier, member);

static if(!hasUDA!(member, Ignore))
//但对大块代码,这很烦人.因为不能用`下`.
{
MemberType memberValue = https://www.songbingjia.com/android/deserialise!MemberType(json[MemberName]);

mixin("toReturn." ~ MemberName ~ " = memberValue; ");
}
}}


??目前??还没有??@名??字段.
实现@名及@按值
static if(!hasUDA!(member, Ignore))
{//修改该函数内容为
JSONValue serialised = serialise(memberValue); //存储在变量中,供未来用.
static if(hasUDA!(member, Name))
//需要时,用自定义名
{
const SerialiseName = getUDAs!(member, Name)[0].name;
toReturn[SerialiseName] = serialised;
}
else // 否则用`字段名`
{
toReturn[MemberName] = serialised;
}
}


反序化:

static if(!hasUDA!(member, Ignore))
{//修改这个块.
static if(hasUDA!(member, Name))
{//名字
const SerialiseName = getUDAs!(member, Name)[0].name;
JSONValue value = https://www.songbingjia.com/android/json[SerialiseName];
}
else
{
JSONValue value = https://www.songbingjia.com/android/json[MemberName];
}

MemberType memberValue = https://www.songbingjia.com/android/deserialise!MemberType(value);

mixin("toReturn." ~ MemberName ~ " = memberValue; ");
}


??按值??:

//注意,在`忽略`中.
static if(!hasUDA!(member, Ignore))
{
// 存储进变量
static if(hasUDA!(member, ByValue) & & is(MemberType == enum))
{//按值.
JSONValue serialised = JSONValue(memberValue);
}
else
{//按名
JSONValue serialised = serialise(memberValue);
}
static if(hasUDA!(member, Name))
{//名字
const SerialiseName = getUDAs!(member, Name)[0].name;
toReturn[SerialiseName] = serialised;
}
else
{
toReturn[MemberName] = serialised;
}
}


同样??反序化??:
【d05用用定属来自定义】
static if(!hasUDA!(member, Ignore))
{

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