The second, probably, will almost certainly be slightly faster, because fewer tasks are logically connected. In the first case, the code is actually equivalent:
MyClass tmp = new MyClass()
tmp.Id = 1;
tmp.Code = "Test";
MyClass c = tmp;
It is very possible that the JIT compiler will overcome this when you declare a new variable - it will not be able to do this if you assign an existing variable with an object initializer.
EDIT: , " " # , . ( JIT ). "" , . .
, , , , .
EDIT: , , , . , - . Urgh. ...
using System;
using System.Diagnostics;
struct BigStruct
{
public int value;
#pragma warning disable 0169
decimal a1, a2, a3, a4, a5, a6, a7, a8;
decimal b1, b2, b3, b4, b5, b6, b7, b8;
decimal c1, c2, c3, c4, c5, c6, c7, c8;
decimal d1, d2, d3, d4, d5, d6, d7, d8;
#pragma warning restore 0169
}
class Test
{
const int Iterations = 10000000;
static void Main()
{
Time(NewVariableObjectInitializer);
Time(ExistingVariableObjectInitializer);
Time(NewVariableDirectSetting);
Time(ExistingVariableDirectSetting);
}
static void Time(Func<int> action)
{
Stopwatch stopwatch = Stopwatch.StartNew();
action();
stopwatch.Stop();
Console.WriteLine("{0}: {1}ms",
action.Method.Name,
stopwatch.ElapsedMilliseconds);
}
static int NewVariableObjectInitializer()
{
int total = 0;
for (int i = 0; i < Iterations; i++)
{
BigStruct b = new BigStruct { value = i };
total += b.value;
}
return total;
}
static int ExistingVariableObjectInitializer()
{
int total = 0;
BigStruct b;
for (int i = 0; i < Iterations; i++)
{
b = new BigStruct { value = i };
total += b.value;
}
return total;
}
static int NewVariableDirectSetting()
{
int total = 0;
for (int i = 0; i < Iterations; i++)
{
BigStruct b = new BigStruct();
b.value = i;
total += b.value;
}
return total;
}
static int ExistingVariableDirectSetting()
{
int total = 0;
BigStruct b;
for (int i = 0; i < Iterations; i++)
{
b = new BigStruct();
b.value = i;
total += b.value;
}
return total;
}
}
( /o +/debug -):
NewVariableObjectInitializer: 3328ms
ExistingVariableObjectInitializer: 3300ms
NewVariableDirectSetting: 1464ms
ExistingVariableDirectSetting: 1491ms
, NewVariableObjectInitializer , ... , # , . , , .