c# - Can I use a TryParse inside Linq Comparable?

Question

A sort of:

Documenti = Documenti
    .OrderBy(o => string.IsNullOrEmpty(o.Note))
    .ThenBy(o => Int32.TryParse(o.Note))
    .ToList();

That will "ignore" (not order, putting at the end) if o.Note is "" or not an int.

How can I do it?

Answer 1

Everyone who uses C#7 or newer scroll to the bottom, everyone else can read the original answer:

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Yes, you can, if you pass the correct parameters to int.TryParse. Both overloads take the int as out-parameter and initialize it inside with the parsed value. So like this:

int note;
Documenti = Documenti
    .OrderBy(o => string.IsNullOrEmpty(o.Note))
    .ThenBy(o => Int32.TryParse(o.Note, out note)) 
    .ToList();

The clean approach is using a method that parses to int and returns int? if unparseable:

public static int? TryGetInt(this string item)
{
    int i;
    bool success = int.TryParse(item, out i);
    return success ? (int?)i : (int?)null;
}

Now you can use this query(OrderByDescending because true is "greater" than false):

Documenti = Documenti.OrderByDescending(d => d.Note.TryGetInt().HasValue).ToList();

It's cleaner than using a local variable that is used in int.TryParse as out parameter.

Eric Lippert commented another answer of me where he gives an example when it might hurt:

C# LINQ: How is string("[1, 2, 3]") parsed as an array?

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Update, this has changed with C#7. Now you can declare the variable directly where you use out parameters:

Documenti = Documenti
.OrderBy(o => string.IsNullOrEmpty(o.Note))
.ThenBy(o => Int32.TryParse(o.Note, out int note)) 
.ToList();