Add a couple of non-canonical ctors

[matklad]

No description provided.

[matklad]

I am not terribly happy about the naming here, but I do thing that we need a ctor with this signature. Doing TextRange(start, start + len) on the callsite doesn't work if start is a non-trivial expression.

[CAD97]

Per discussion in #2, the construction patterns we want to make easy (but I'm up to changing these targets):

• "of anchored text"
• "of text at offset"
• "empty at offset"
• "start and end"

The currently implemented ways on master to achieve this:

• "of anchored text" ⟹ TextRange(TextSize::zero(), TextSize::of(text))
• "of text at offset" ⟹ TextRange(offset, offset + TextSize::of(text))
• "empty at offset" ⟹ TextRange(offset, offset)
• "start and end" ⟹ TextRange(start, end)

(TextSize::of may be of course replaced with whatever text.len() the text object provides.)

With this PR, we have:

• "of text at offset" ⟹ TextRange::offset_len(offset, TextSize::of(text))
• "empty at offset" ⟹ TextRange::empty(offset)

Counter proposal 1 – TextRange::anchored:

• "of anchored text" ⟹ TextRange::anchored(TextSize::zero(), text)
• "of text at offset" ⟹ TextRange::anchored(offset, text)

Counter proposal 2 – TextRange::offset, which is needed anyway to reintroduce Add::add functionality:

• "of anchored text" ⟹ TextRange::of(text)
• "of text at offset" ⟹ TextRange::of(text).offset(offset)

Counter proposal 3 – factory style length replacement TextRange::with_len:

• "of text at offset" ⟹ TextRange::at(offset).with_len(TextSize::of(text))
• "empty at offset" ⟹ TextRange::at(offset)

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I think TextRange::at(offset) reads marginally better than TextRange::empty(offset), though the latter is arguably more intent-clear. I agree we need an "offset_len", but I'm not willing to accept that name without exploring the design space a bit more.

[matklad]

I do feel that TextRange::empty is much better than TextRange::at. To me, the latter makes sense only with combination with with_len (and that calls for a dedicated at_with_len or somthing function).

I agree we need an "offset_len", but I'm not willing to accept that name without exploring the design space a bit more.

I now think that, with TextRange::empty, I wouldn't miss offset_len that much. Like, we still need it, but we can make progress without.

[matklad]

Hm, I am starting to think that maybe TextRage::offset_len(start, len) should be spelled as TextRange::xxx(len) + start, but I don't know a good name for xxx. Like, it should be the dual of empty, where start, and not length, is zero. TextRange::to(offset)?

[kjeremy]

with_offset?

[matklad]

Are you talking about my xxx? That should be exactly the opposite, with_len

[CAD97]

On a previous branch, I had it as TextRange::of(text: impl TextSized) => TextRange(0..text.len()). I don't know how obvious that naming is anymore, but just to throw it back out there.

[matklad]

I am more concerned not with the naming, but with the fact that the argument should be a TextSize and not impl TextSized.