Proposal: Binary literals

[MadsTorgersen]

There’s a relatively common request to add binary literals to C# and VB. For bitmasks (e.g. flag enums) this seems genuinely useful, but it would also be great just for educational purposes.

Binary literals would look like this:

int nineteen = 0b10011;

Syntactically and semantically they are identical to hexadecimal literals, except for using b/B instead of x/X, having only digits 0 and 1 and being interpreted in base 2 instead of 16.

There’s little cost to implementing these, and little conceptual overhead to users of the language.

Syntax

The grammar would be as follows:

integer-literal:
  ...
  binary-integer-literal

binary-integer-literal:
  0b   binary-digits   integer-type-suffixopt
  0B   binary-digits   integer-type-suffixopt

binary-digits:
  binary-digit
  binary-digits   binary-digit

binary-digit:   one of
  0 1

[monoman]

👍

[AdamSpeight2008]

A think a digit separator would also help. _
0b_10000000_00000000_00000000_0000_0000

[ddevault]

👍

[alanfo]

Good idea and, whilst you're at it, why don't you add octal literals as well?

VB and F# already support these which are still occasionally useful when doing interop with older unmanaged code or translating it to C#.

Perhaps a prefix of '0o' or '0O' followed by the octal digits would be a suitable syntax as this is what F# and Swift use.

[tmat]

@alanfo I don't think we should add new features like octal literals to C# whose only benefit is to make somewhat convenient to deal with legacy code.

[ddevault]

That's not the only benefit. I would benefit from this in several modern projects. Anything that uses bitwise math stands to gain a lot from binary literals. Here are a couple of examples:

• These numbers make more sense in binary than in hex
• Ditto

[ddevault]

Mask out the lower five bits - & 0xE0 or & 0b11100000?

[tmat]

@SirCmpwn I meant octal, not binary. Binary literals are certainly useful. My comment perhaps wasn't clear.

[ddevault]

@tmat no worries. An obvious use case that comes to mind for octal is Unix file permissions.