Is there any way in C# to create a variable inline? Something like this:
int x = int.TryParse("5", out new int intOutParameter) ? intOutParameter : 0;
Don´t you think that this is more useful than creating a variable outside and then never use it again?
That syntax – called declaration expressions – was on the proposed feature list for the next version of C# (version 6).
You're not the only one to think it is useful. For instance making a complete TryParse call an expression (no need for a statement to declare the variable).
However it has been dropped from the ongoing work to C#6.
I'm sure I'm not the only one hoping it will make a return in a future version.It is included in C#7 as a declaration (no need for new):
int x = int.TryParse("5", out int intOutParameter) ? intOutParameter : 0;
Inline declarations for out params is a new suggested feature in C# that might be standard one day, see e.g. Probable C# 6.0 features illustrated, section 9. The expected/proposed syntax:
int.TryParse("5", out int x); // this declares (and assigns) a new variable x
Edit: This out variable syntax was eventually included in C# 7.0 (Visual Studio 2017); you can also use out var x.
Addition: People come up with fun extension methods. I tried to make a generic one:
public delegate bool TryParser<TResult>(string s, out TResult result);
public static class FunExtensions
{
public static T TryParse<T>(this string str, TryParser<T> tryParser)
{
T outResult;
tryParser(str, out outResult);
return outResult;
}
}
This can be used like this:
var x = "5".TryParse<int>(int.TryParse);
var y = "01/01".TryParse<DateTime>(DateTime.TryParse);
var z = "bad".TryParse<decimal>(decimal.TryParse);
and so on. I was hoping the compiler would infer T from usage, so that one could say simply:
var x = "5".TryParse(int.TryParse); // won't compile
but it appears you have to explicitly specify the type argument to the method.
As a workaround you could create an extension:
public static int TryParse(this string input, int defaultValue = default(int))
{
int intOutParameter;
bool parsable = int.TryParse(input, out intOutParameter);
if (parsable)
return intOutParameter;
else
return defaultValue;
}
Then you don't even need an out-parameter:
int parsed = "5".TryParse(0);
Guid.TryParse and TimeSpan.TryParse etc. I tried a generic extension in my answer.Based on OP request:
private static bool IsIntValid(string str)
{
int i = 0;
return int.TryParse(str, out i);
}
Granted not the most cleverest approach however, the simplest I guess :) Can wrap this in an extension method also perhaps.
You can also use a temporary storage for all methods.
public static class Tmp<T>
{
[ThreadStatic]
public static T Value;
}
int x = int.TryParse("5", out Tmp<int>.Value) ? Tmp<int>.Value : 0;
