Why is there an overload for String.Concat() which accepts one parameter in .NET

Question

Noticed this today when a patch was submitted with the following line:

lblCompletionTime.Text = String.Concat(trainingSkill.EndTime.ToLocalTime())

I can understand why the contributor used that syntax as above line concatenated two strings to form a multi-part date/time string.

Is there some hidden reason for having a single parameter overload of String.Concat() or was it included for "completeness" by the language designers.

I have replaced the line with:

lblCompletionTime.Text = trainingSkill.EndTime.ToLocalTime().ToString(CultureInfo.CurrentCulture)

Which has the same output.

Martin v. Löwis · Accepted Answer · 2009-08-28 20:00:36Z

10

String.Concat(Object) gives you String.Empty when you pass null; ToString would crash with a null pointer exception.

answered Aug 28, 2009 at 20:00

Martin v. Löwis

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2 Comments

Pierre-Alain Vigeant Over a year ago

What's funny is that they could make ToString an extension method on Object so that even calling myObject.ToString() when myObject is null would work.

STW Over a year ago

@Pierre: "can" is rarely a good reason without a supporting "should"

Andrew Hare · Accepted Answer · 2009-08-28 20:01:21Z

4

I agree that it doesn't make much sense especially considering the fact that this is the implementation:

public static string Concat(object arg0)
{
        if (arg0 == null)
        {
                return Empty;
        }
        return arg0.ToString();
}

But it does validate that the argument isn't null so I guess that is something. Still you aren't concatenating anything so I think that this method could have been called

String.ToStringSafe(Object obj) { }

or something similar to better express what the function actually does.

answered Aug 28, 2009 at 20:01

Andrew Hare

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Comments

Charlie Salts · Accepted Answer · 2009-08-28 19:59:19Z

3

According to MSDN, String.Concat(object)

Creates the String representation of a specified object.

answered Aug 28, 2009 at 19:59

Charlie Salts

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1 Comment

Richard Slater Over a year ago

Object.ToString() says more or less the same thing. "Returns a String that represents the current Object.". I had realised what it did, it was more the why that I was interested in.

pauloya · Accepted Answer · 2009-08-28 20:09:16Z

2

By looking at the documentation of String.Concat(object), the only advantage I see is that it accepts a null and returns an empty string, which can be an advantage when compared with object.ToString() which would throw a NullReferenceException. In your example it doesn't help because if trainingSkill.EndTime is null the program will break when invoking ToLocalTime. I preffer your correction, but I think there's no need for passing CultureInfo.CurrentCulture as a parameter since it is the default behaviour of DateTime.ToString()

answered Aug 28, 2009 at 20:09

pauloya

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2 Comments

Richard Slater Over a year ago

The default behaviour seems a litle inconsitant particuarly on certain european installs .ToString will default to en-US, in fact FxCop will recommend replacing all instances of int.ToString(), DateTime.ToString() with the equavalant Overload that accepts an IFormatProvider.

pauloya Over a year ago

According to documentation both DateTime.ToString() and CurrentInfo.CurrentCulture use Thread.CurrentThread.CurrentCulture. So using DateTime.ToString(CurrentInfo.CurrentCulture) should always equal DateTime.ToString().

Austin Salonen · Accepted Answer · 2009-08-28 20:11:23Z

1

In C# it may have little value (aside from the automatic empty string for a null value).

In .Net in general, I could this method signature being very useful in a functional language.

answered Aug 28, 2009 at 20:11

Austin Salonen

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3 Comments

Richard Slater Over a year ago

That is an interesting slant on the thought, I must admit I havn't looked at .NET based functional programming. What would stop you from using .ToString() in say F#?

Austin Salonen Over a year ago

For a single object, ToString would make sense; but if it's processing a list recursively (Head | Tail -- probably not F# syntax but you get the idea), it will call the same function on both -- one being a single object, the other a list, or null.

Austin Salonen Over a year ago

FWIW, this is just a gut instinct. I have no proof that it actually works this way.

Sebastian Paaske Tørholm · Accepted Answer · 2009-08-28 20:01:26Z

0

Using String.Concat(Object) to convert an object to a string is the behavior that overload of the function was designed for.

String.Concat Method (Object)
Creates the String representation of a specified object.

answered Aug 28, 2009 at 20:01

Sebastian Paaske Tørholm

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