[英]delphi Using records as key in TDictionary
Can you use a record as a Key value in TDictionary? TDictionary 中可以使用记录作为 Key 值吗? I want to find objects based on combination of string, integer and integer.我想根据字符串、整数和整数的组合来查找对象。
TUserParKey=record
App:string;
ID:integer;
Nr:integer;
end;
... ...
var
tmpKey:TUserParKey;
tmpObject:TObject;
begin
tmpObject:= TTObject.Create(1);
tmpKey.App:='1';
tmpKey.ID :=1;
tmpKey.Nr :=1;
DTUserPars.Add(tmpKey,tmpObject)
... ...
var
tmpKey:TUserParKey;
begin
tmpKey.App:='1';
tmpKey.ID :=1;
tmpKey.Nr :=1;
if not DTUserPars.TryGetValue(tmpKey,Result) then begin
result := TTObject.Create(2);
end;
This returns object 2.这将返回对象 2。
Yes, you can use records as keys in a TDictionary but you should provide your own IEqualityComparer when creating the dictionary because the default one for records just does a dumb binary compare of the record.是的,您可以将记录用作 TDictionary 中的键,但您应该在创建字典时提供自己的 IEqualityComparer,因为记录的默认值只是对记录进行愚蠢的二进制比较。 This fails for a record containing a string because it just compares the pointer of that string which may be different even if the string contains the same value.这对于包含字符串的记录失败,因为它只是比较该字符串的指针,即使该字符串包含相同的值,该指针也可能不同。
Such a comparer would look like this:这样的比较器看起来像这样:
type
TUserParKeyComparer = class(TEqualityComparer<TUserParKey>)
function Equals(const Left, Right: TUserParKey): Boolean; override;
function GetHashCode(const Value: TUserParKey): Integer; override;
end;
function TUserParKeyComparer.Equals(const Left, Right: TUserParKey): Boolean;
begin
Result := (Left.App = Right.App) and (Left.ID = Right.ID) and (Left.Nr = Right.Nr);
end;
function TUserParKeyComparer.GetHashCode(const Value: TUserParKey): Integer;
begin
Result := BobJenkinsHash(PChar(Value.App)^, Length(Value.App) * SizeOf(Char), 0);
Result := BobJenkinsHash(Value.ID, SizeOf(Integer), Result);
Result := BobJenkinsHash(Value.Nr, SizeOf(Integer), Result);
end;
Instead of using the record as a key, you could use a string consisting of the serialized record.您可以使用由序列化记录组成的字符串,而不是使用记录作为键。 You could use something like https://github.com/hgourvest/superobject to do the serialization.您可以使用类似https://github.com/hgourvest/superobject 的东西来进行序列化。
Since strings have built-in comparison semantics and hashcodes, you don't need to write comparison and hashcode functions.由于字符串具有内置的比较语义和哈希码,因此您无需编写比较和哈希码函数。
My best approach should be to joint the default hash code of the base types.我最好的方法应该是联合基本类型的默认哈希码。
For instance:例如:
Value.App.GetHashCode + Value.ID.GetHashCode + Value.Nr.GetHashCode;
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