Can I avoid an unnecessary variable being created in this function?

Question

I have got a very simple function that takes anything in as an object, but generally a string, and attempts to format it in a specific date format that we use for reports at work.

The function is generally called using the OnRowDataBound event of a GridView and returns the date as a string if it could parse it or the original input as a string.

Here is the function:

public string FormatDate(object input)
{
    DateTime output;

    return DateTime.TryParse(input.ToString(), out output)
        ? output.ToString("dd-MMM") : input.ToString();
}

Maybe I am being picky but the issue I have is the creation of a variable, in this case a DateTime object called output, which is created purely for the output of the TryParse function which I then convert to string in the format I specify.

Is there a better, more concise method of doing this?

Answer 1

I don't see what the purpose would be. Any more concise than that and it'd be difficult to read. That said, if you switched to DateTime.Parse you could just return that outright. Of course, then you would have to worry about the exception if it failed.

Answer 2

I'm afraid not, since it's an out parameter and the variable will have to be declared on the stack. I'm a little surprised by your code though, if you get a date you format it, and if the parsing fails you just display the string as-is?

Answer 3

You can't get away from the extra variable instantiation, but you can hide it with a helper method:

public static string DateTimeParseOrDefault(this object input, string format, string def) {
    DateTime output;
    return DateTime.TryParse(input.ToString(), out output)
        ? output.ToString(format)
        : def;
}

Which you then call in your function as:

public string FormatDate(object input) {
    return input.DateTimeParseOfDefault("dd-MMM", input.ToString());
}

You'll probably want to rename that goofy function name, or perhaps not use an extension method (just a regular static method) - but it's up to you at this point. Again all you're doing here is hiding the variable.

Answer 4

Roll that logic into your tryParse method, so it returns the correct thing right away. Right now TryParse returns a boolean. Why can't it just return the final string value? Maybe you can create an overridden or overloaded version of it if you need to.

Answer 5

Since the DateTime.TryParse() function requires the output variable, I don't see a way to get around creating the output variable there...

You could use the Parse() function instead with a try, catch... I'm not a big fan of this in general and try to avoid this type of stuff...

    try
    {
        this.label1.Text = DateTime.Parse(this.textBox1.Text).ToString("dd-MMM");
    }
    catch (FormatException)
    {
        this.label1.Text = this.textBox1.Text;
    }

EDIT
Erik had a good point, in catching the specific exception. It was a code sample which is why I left it at Exception. Use FormatException if you use this...

Answer 6

I don't think there is.

remember the TryParse is communicating 2 results (1.did the parse succeed and 2. the datetime value if it did), but has only one return value.

Using Parse would make you deal with the exception. You can save the input.ToString, it's already a string.

Answer 7

You are referencing output in two places. How could it not be a variable?

I'd be more worried about the exceptions which will happen when someone passes a null value for input.

Also, since your method explicitly works with string only, you should communicate that in your API by accepting a string instead of an object. Let the caller of the method determine how they would like to supply the string instance.

Answer 8

First, I see a problem with the method name. It is called 'FormatDate(...)' I would expect the parameter to be a DateTime field. Taking in an object type makes the method harder to understand. With out knowing the code/implementation I wouldn't know what I would get back if I sent it an ArrayList object or a Person object. There isn't a logical answer. I think rewritting the method to Format a Date and only taking in a DateTime object makes the method clear and eliminates all of the variables.

public string FormatDate(DateTime date) 
{    
    return date.ToString("dd-MMM")
}

Look into "Working Classes" in Code Complete 2 by Steve McConnell. He discusses this with Chaper 6 I belive.