Add StringBuilder(Char)

[iSazonov]

Rationale

In PowerShell repo we got a report PowerShell/PowerShell#3457 about

var allErrors = new StringBuilder('\n');

It is expected that allErrors initialized with '\n' char.
Really compiler silently convert the char -> ushort -> int and use StringBuilder(int capacity) constructor.
Sample http://ideone.com/1pPHlZ

Currently we already have method Append(char value) so suggestion is to add new constructor StringBuilder(char value).

Proposed API

public sealed partial class StringBuilder : ISerializable 
{ 
        // Proposed constructor
        public StringBuilder(char value);
}

[karelz]

@iSazonov it makes sense to me. Can you please format it into a formal API proposal? It is just much easier to read and review in larger group. Thanks!

[iSazonov]

@karelz Issue was reformatted.

[karelz]

Thanks! I let area owners to check it. From my perspective it is ready for larger API review.

[terrajobst]

This is a good point. The same problem would also exist for this piece of code:

var allErrors = new StringBuilder(' ', 8);

So I suggest we add these two:

public partial class StringBuilder 
{ 
    public StringBuilder(char value);
    public StringBuilder(char value, int repeatCount);
}

@stephentoub mentioned that the sheer fact of us exposing these APIs might cause more issues, when people multi-target and now end up calling the "wrong" APIs. There is also the meta problem that this is a battle we just can't win; C# has an implicit conversion from char to int, so maybe be should just bite the bullet and accept this as a fact of life.

[danmoseley]

Ouch, I'm surprised this didn't come up before.

[terrajobst]

Video

So after discussion we think it's not worth it. It's been 20 years and this isn't a widespread enough problem.