StringBuilder: char constructor

[eduherminio]

After (painfully) realizing that certain StringBuilder constructor accepts a char, but not the one I was expecting to, I'm now wondering whether adding the following constructor to StringBuilder has ever been considered:

public StringBuilder(char? value)

This is a simplified version of the code that brought me here:

var str = "ABC";
var sb = new StringBuilder(str.Last());

Console.WriteLine($"-->{sb.ToString()}<--");

Thanks!

[PathogenDavid]

I feel like this isn't a common enough situation to justify adding a new API. I'm assuming you need a StringBuilder in this situation (if not, the StringBuilder is adding a ton of overhead for a single character string and you should just use str.Last().ToString().)

If you need to allocate a single-character StringBuilder and you want to do so efficiently, you can explicitly specify the initial capacity to be 1. IE:

var str = "ABC";

var sb = new StringBuilder(1);
sb.Append(str.Last());

[eduherminio]

I would have said that initializing a StringBuilder with a char would be a relatively common situation, but if no one proposed it before, I guess you're right and it's not 🤷🏼‍♂️.

I still think that it would be great to avoid the current behavior difference beween new StringBuilder("a") and new StringBuilder('a').

PD: as stated, that was a simplified version of the code, the StringBuilder instance was initialized with a specific char, but appended large strings chunks afterwards.

[PathogenDavid]

I still think that it would be great to avoid the current behavior difference beween new StringBuilder("a") and new StringBuilder('a').

I would not expect there to be a significant performance difference if the single-character string passed in is constant. If the difference is impactful enough to matter to you, you probably shouldn't even be using StringBuilder in the first place.

Oops, I thought this was about a perceived performance difference. I didn't originally read this correctly:

After (painfully) realizing that certain StringBuilder constructor accepts a char, but not the one I was expecting to

What unfortunately happened was the char was implicitly cast to int. So it called the initial-capacity constructor.

Unfortunately that means adding a new constructor would break existing code. (Even if that code is probably incorrect.)

This was proposed before as #20848 and was rejected. You can watch the design review for their reasoning here: https://youtu.be/JdaQ2RP2tqM?t=6187

I think this could be something that could make sense as an analyzer. Possibly even as one of the analyzers in Microsoft.CodeAnalysis.NetAnalyzers.

[eduherminio]

I somehow missed that issue 😓 thanks @PathogenDavid!

[PathogenDavid]

No problem! I've found it helps to restrict the search to the titles of issues. I found it using is:issue stringbuilder char in:title

[danmoseley]

Feel free to open issue proposing an analyzer.

[danmoseley]

BTW I wished to mark @PathogenDavid's 2nd response above as the "Answer" but it seems one cannot tag responses to comments as answers.

[PathogenDavid]

Yeah, I probably should've posted that part separately. I extracted the answer half of that comment into a proper answer if you still want to mark it for the sake of posterity.

[danmoseley]

done!

[eduherminio]

Awesome, I opened #46103 for it, don't know why GH isn't linking it here though.
Thanks!

[PathogenDavid]

After (painfully) realizing that certain StringBuilder constructor accepts a char, but not the one I was expecting to

What unfortunately happened was the char was implicitly cast to int. So it called the initial-capacity constructor.

Unfortunately that means adding a new constructor would break existing code. (Even if that code is probably incorrect.)

This was proposed before as #20848 and was rejected. You can watch the design review for their reasoning here: https://youtu.be/JdaQ2RP2tqM?t=6187

I think this could be something that could make sense as an analyzer. Possibly even as one of the analyzers in Microsoft.CodeAnalysis.NetAnalyzers.