117 lines
2.8 KiB
Markdown
117 lines
2.8 KiB
Markdown
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# C# Language Design Notes for Jan 22, 2018
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***Warning: These are raw notes, and still need to be cleaned up. Read at your own peril!***
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# Range
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``` c#
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var numbers = ints[from..to];
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```
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Should this mean inclusive?
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Not many languages have *only* inclusive ranges. Apart from F#, they tend to either have exclusive ranges or both (at the upper end; the lower is always inclusive).
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Python has exclusive, though a lot of people seem to be confused about it.
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```
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var s = a[0..a.Length];
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```
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Do we read it out loud as "zero *to* a dot length"? If so, then the intuition really does suggest inclusive.
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```
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foreach (var x in 1..100) { ... }
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foreach (var x in 0..100) { ... }
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```
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You don't use constants in practice, though, except as a zero lower bound. In F# it is often a bit of a pain for do a for loop for array iteration, for instance.
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Exclusive is "in the middle" between inclusive and start/length.
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``` c#
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// The three scenarios with exclusive
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Range incl = start..end+1;
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Range excl = start..end;
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Range rel = start..start+length;
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Range emp = 0..0;
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// The three scenarios with inclusive
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Range incl = start..end;
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Range excl = start..end-1;
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Range rel = start..start+length-1;
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Range emp = 0..-1;
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// The three scenarios with start/length
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Range incl = start:end-start+1;
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Range excl = start:end-start;
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Range rel = start:length;
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Range emp = 0:0;
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```
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[1/22/2018 10:27 AM] Miguel de Icaza:
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From the TensorFlow (504), NUmPy (1,063) - both numeric heavy- and Python’s core libraries (2,094). Only one use of “end-range plus one”, ie, used in exlusive way
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[1/22/2018 10:31 AM] Miguel de Icaza:
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More data for you: in F#’ compiler source code, out of 1,034 uses of ranges, 51 use the idiom limit-1
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[1/22/2018 10:32 AM] Miguel de Icaza:
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Fixed: 64 out of 1,034
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[1/22/2018 10:39 AM] Miguel de Icaza:
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Go source code, out of 5865, 11 need “+1”
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One idea is that when we start talking about sets of numbers (not enumerations) we should just have a different syntax. That's in pattern matching/containment checking, etc.
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``` c#
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x is in 3 to 5;
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x is in 3--5;
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x is in 3 !.. 5
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```
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Tensors are really just multidimensional arrays, so similar arguments apply.
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Let us go with `..` means exclusive.
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## Open ended
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Is represented as such in the type. Syntax:
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``` c#
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Range openL = ..5;
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Range openR = 3..;
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Range openLR = ..;
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```
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``` c#
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r1 = ..12;
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r2 = 3..;
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var a = new int[5];
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a[r2]; // fine
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a[r1 * r2]; // fail;
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Range x = new Range(r1.Start, r2.End);
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Range x = r1.EndAt(r2);
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```
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Would like not to write conditional logic to manipulate and combine ranges.
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## Natural type
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``` c#
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var r = 4..6; // infer Range
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```
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If we do this, `Range` will be forever tied to it as the preferential type.
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We're good with that.
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## Start/length
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Can technically be added later, but if we want to do it we should try to do it now.
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