我想有一個字典,當找不到搜索關鍵字時返回默認值。從文檔中讀取:德爾福泛型>字典默認值
Generics.Collections.Tdictionary [...]該類提供了映射和初始內容。
1 - 如何?有沒有辦法做到這一點Python:{1:'one'; 2:'two'}?
Generics.Collections.TDictionary.TryGetValue [...] TryGetValue返回true,如果給定的鍵在字典中並在Value中提供其值。否則,它返回false,並將Value設置爲Tvalue的默認值類型。
2 - 如何設置此默認值?我找不到一個構造函數(可能是我剛纔在錯誤的地方搜索過的,我期待類似於「構造函數Create(DefaultValue:TValue);」)
所以我試圖實現我自己的(可能是沒有必要見上文):(!評論和建議,歡迎)
的代碼是:
unit Util;
interface
uses
Generics.collections;
type
//
// Dictionary with default response
//
TDefaultDictonary<K, V> = class(TObjectDictionary<K, V>)
private
M_DefaultValue : V;
public
constructor Create(Defaultvalue : V);
destructor Destroy; reintroduce;
function GetDefaultValue : V;
function TryGetValue(const Key: K; out Value: V): Boolean;
function GetValueOf(const Key: K) : V;
end;
implementation
//
// Contructor and destructor
//
constructor TDefaultDictonary<K, V>.Create(Defaultvalue : V);
begin
inherited Create;
M_DefaultValue := Defaultvalue;
end;
destructor TDefaultDictonary<K, V>.Destroy;
begin
inherited Destroy;
end;
//
// Get the default Value
//
function TDefaultDictonary<K, V>.GetDefaultValue : V;
begin
Result := M_DefaultValue;
end;
//
// Try to get a value from the dictionary for the given key.
//
// If the value is found then "Value" holds it and the function returns true.
// If the value is not found then "Value" holds the default value and the
// function returns false.
//
function TDefaultDictonary<K, V>.TryGetValue(const Key: K; out Value: V): Boolean;
var
IsKeyFound : boolean;
DictVal : V;
begin
IsKeyFound := inherited TryGetValue(Key, DictVal);
if not IsKeyFound then begin
DictVal := M_DefaultValue;
end;
// Outputs:
Value := DictVal;
Result := IsKeyFound;
end;
//
// Get a value from the dictionary for the given key.
//
// If the value is found then the function returns it.
// If the value is not found the function returns the default value.
//
function TDefaultDictonary<K, V>.GetValueOf(const Key: K) : V;
var
DictVal : V;
begin
TryGetValue(Key, DictVal);
Result := DictVal;
end;
,測試開始:
unit Test_Utils;
{
Test the TDefaultDictionary functionality
}
interface
uses
Sysutils, Math, TestFramework, Util;
type
TestUtil = class(TTestCase)
public
procedure SetUp; override;
procedure TearDown; override;
published
procedure TestDefaultDictionaryGetDefaultResponse;
procedure TestDefaultDictionaryExistingKey;
procedure TestDefaultDictionaryNotExistingKey;
end;
implementation
procedure TestUtil.SetUp;
begin
end;
procedure TestUtil.TearDown;
begin
end;
procedure TestUtil.TestDefaultDictionaryGetDefaultResponse;
var
dd : TDefaultDictonary<integer, string>;
begin
dd := TDefaultDictonary<integer, string>.Create('Default response');
checkEquals('Default response', dd.GetDefaultValue);
dd.Free;
end;
procedure TestUtil.TestDefaultDictionaryExistingKey;
var
dd : TDefaultDictonary<integer, string>;
outVal : string;
isKeyFound : boolean;
begin
dd := TDefaultDictonary<integer, string>.Create('Default response');
dd.Add(1, 'My one');
checkEquals(1, dd.Count,
'One element as count');
isKeyFound := dd.TryGetValue(1, outVal);
check(isKeyFound,
'Key not found by TryGetValue');
checkEquals('My one', outVal,
'Value given by TryGetValue');
checkEquals('My one', dd[1],
'Value given by indexing as array');
dd.Free;
end;
procedure TestUtil.TestDefaultDictionaryNotExistingKey;
var
dd : TDefaultDictonary<integer, string>;
outVal : string;
isKeyFound : boolean;
begin
dd := TDefaultDictonary<integer, string>.Create('Default response');
dd.Add(1, 'one');
isKeyFound := dd.TryGetValue(2, outVal);
check(not isKeyFound,
'Key should not be found by TryGetValue');
checkEquals('Default response', outVal,
'Default Value given by TryGetValue');
checkEquals('Default response', dd.GetValueOf(2),
'Default Value given by indexing as array');
//
// It is possible to oveload the indexer operator?
// Please review or delete me !
//
//checkEquals('Default response', dd[2],
// 'Value given by indexing as array');
//
dd.Free;
end;
initialization
RegisterTest(TestUtil.Suite);
end.
,從很遠完成。我想讓索引運算符也工作(參見最後一個測試)。這可能嗎?還應該執行什麼?
這個實現是否泄漏M_DefaultValue(我是Delphi新手)。我不能在析構函數中做一些M_DefaultValue.Free(由於構造函數約束不太靈活)可以在這裏做什麼?
由於提前,
弗朗西斯
您提出了一個非常好的問題,因爲目前在Delphi中,我們必須做兩個字典查找。關於PHP也是如此。 – 2017-05-16 00:52:46