code review 125540043: go.blog: constants

go.blog: constants

[gri, 2014-08-20 00:32:10]

LGTM but several comments.

As an aside: I was thinking it would be nice if one could use //line comments to
force error message for the blog examples show up with line numbers matching the
example, as in:

http://play.golang.org/p/pj5jYFj8Xw

Unfortunately, the error message also shows the real location in []'s. Perhaps
we could filter those out for playground/etc. compiler errors?

https://codereview.appspot.com/125540043/diff/20001/content/constants.article
File content/constants.article (right):

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:34: When designing Go, we decided to avoid this whole
minefield by mandating that there is _no_ mixing of numeric types.
s/whole minefield/minefield entirely/ (?)

reads more smoothly (to my ears)

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:63: Such values, named or otherwise, are called
_constants_ in Go.
There's no mention of constant expressions, but they are creeping in later, as
in 1 + 0i. Perhaps just add `2 + 3` as another example?

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:86: This is an _untyped_string_constant_, which is to
say it is a constant value holding some text, but it does not have a fixed type
yet.
a constant value of text

or:

a constant text value

(the value is the text, it's not holding it)

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:155: One way to think about untyped constants is that
they live in a kind of ideal space of values, a space not tied to Go's type
system.
s/tied to/constrained by/

or even

s/tied to/much less constrained by/

Constants after all are very much tied to Go's type system, but it's much less
restrictive.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:171: to pass as an argument, and the concrete type
stored of that argument is the default type of the constant.
s/of that/for that/ (?)

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:226: Numeric constants live in an arbitrary-precision
numeric space; they are just abstract numbers.
s/abstract// (?)

I'd say an abstract number is 'x' while '42' is a concrete number...

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:237: But `Huge` might be useful, and we can compute
with it and use the result of that computation if the result
we can compute with it: another place where you have a constant expression - a
careful reader not familiar with Go might wonder where this computation happens
- before you said there's not much that can be done with constants

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:237: But `Huge` might be useful, and we can compute
with it and use the result of that computation if the result
s/can compute with it/express arithmetic with it/ (?)

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:245: In a related way, floating-point constants may
have very high precision, so that calculations involving them are more accurate.
so that arithmetic involving them is more accurate.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:261: soft underflows, and `NaNs` to arise in constant
expressions.
s/to // (?)

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:346: Here is an informative little exercise
missing : at end

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:361: but that is illegal because the abstract number
-1 cannot be represented by an unsigned variable; `-1` is not in the range of
unsigned values.
s/abstract // (?)

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:366: Even though at run-time a value of -1 can be
converted to an unsigned integer, the rules of constants forbid this kind of
coercion at compile time.
s/of constants/for constant conversions/

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:382: The solution is to tell Go how many bits to use
to represent the `0`, and invert that.
I've read this section now 3x, and each time I'm doing a double-take. The first
part of the first sentence doesn't make sense to me (even though I know what you
want to say), and the 2nd half doesn't explain why this solves the problem. The
rest builds on this.

How about:

We know that the largest unsigned integer value has all `1` bits set. The prior
attempts (-1, ^0) don't work because the operations (negation, inversion)
operate on untyped numbers, resulting in untyped negative numbers which don't
fit into a uint. So we must avoid negative values. One way to achieve that is to
start with uint(0), the unsigned integer 0. We are now in "unsigned integer
land", and flipping the bits using `^uint(0)` will result in another unsigned
integer value of all 1's.

(or some such)

As an aside: In these examples you use constant expressions throughout (incl.
conversions). Perhaps making clear that such expressions remain constants may be
warranted earlier, despite attempts to keep it as simple as possible.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:404: All these constants have numeric value 1
missing : at end ?

[adg, 2014-08-20 01:30:39]

https://codereview.appspot.com/125540043/diff/20001/content/constants.article
File content/constants.article (right):

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:167: func Printf(a ...interface{}) (n int, err error)
you use Printf here but this signature is actually Print or Println's.
Either the above example code should be
  fmt.Printf("%v\n", "Hello")
or
  fmt.Println("Hello")

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:191: For string constants, it's obvious that the
implicit type is `string`.
how about "For string constants, the only possible implicit type is string."

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:193: Integer constants default to `int`,
floating-point constants `float64`, rune constants to `rune` (an alias for
`int32`), imaginary constants to `complex128`, and so on.
link "alias' to http://golang.org/ref/spec#Numeric_types ?

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:289: prints `complex128:` `(2+0i)`.
this fragment doesn't follow from the previous sentence

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:302: They have more moving parts—many sizes, signed or
unsigned, and more—but they play by the same rules.
maybe another place to link the numbers section of the spec

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:336: .play -edit constants/int3.go /var/
show a large number assignment, too?

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:348: The number of bits available depends on the
architecture, so we can't just write down a single value.
this sentence should be part of the text after the MaxUint32 decl

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:355: Fans of 2's-complement arithmetic, which Go's
integers are defined to use, know that the representation of `-1` has all its
bits set to 1, so the bit pattern of `-1` is internally the same as that of the
link to http://en.wikipedia.org/wiki/Two's_complement ?

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:393: Whatever the number of bits it takes to represent
a `uint` in the current execution environment (on the playground, it's 32),
link to //blog.golang.org/playground

[r, 2014-08-20 16:06:20]

https://codereview.appspot.com/125540043/diff/20001/content/constants.article
File content/constants.article (right):

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:34: When designing Go, we decided to avoid this whole
minefield by mandating that there is _no_ mixing of numeric types.
On 2014/08/20 00:32:10, gri wrote:
> s/whole minefield/minefield entirely/ (?)
> 
> reads more smoothly (to my ears)

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:63: Such values, named or otherwise, are called
_constants_ in Go.
On 2014/08/20 00:32:10, gri wrote:
> There's no mention of constant expressions, but they are creeping in later, as
> in 1 + 0i. Perhaps just add `2 + 3` as another example?

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:86: This is an _untyped_string_constant_, which is to
say it is a constant value holding some text, but it does not have a fixed type
yet.
On 2014/08/20 00:32:10, gri wrote:
> a constant value of text
> 
> or:
> 
> a constant text value
> 
> (the value is the text, it's not holding it)

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:155: One way to think about untyped constants is that
they live in a kind of ideal space of values, a space not tied to Go's type
system.
On 2014/08/20 00:32:10, gri wrote:
> s/tied to/constrained by/
> 
> or even
> 
> s/tied to/much less constrained by/
> 
> Constants after all are very much tied to Go's type system, but it's much less
> restrictive.

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:167: func Printf(a ...interface{}) (n int, err error)
On 2014/08/20 01:30:39, adg wrote:
> you use Printf here but this signature is actually Print or Println's.
> Either the above example code should be
>   fmt.Printf("%v\n", "Hello")
> or
>   fmt.Println("Hello")

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:171: to pass as an argument, and the concrete type
stored of that argument is the default type of the constant.
On 2014/08/20 00:32:10, gri wrote:
> s/of that/for that/ (?)

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:191: For string constants, it's obvious that the
implicit type is `string`.
On 2014/08/20 01:30:39, adg wrote:
> how about "For string constants, the only possible implicit type is string."

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:193: Integer constants default to `int`,
floating-point constants `float64`, rune constants to `rune` (an alias for
`int32`), imaginary constants to `complex128`, and so on.
On 2014/08/20 01:30:38, adg wrote:
> link "alias' to http://golang.org/ref/spec#Numeric_types ?

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:226: Numeric constants live in an arbitrary-precision
numeric space; they are just abstract numbers.
On 2014/08/20 00:32:10, gri wrote:
> s/abstract// (?)
> 
> I'd say an abstract number is 'x' while '42' is a concrete number...

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:237: But `Huge` might be useful, and we can compute
with it and use the result of that computation if the result
On 2014/08/20 00:32:10, gri wrote:
> s/can compute with it/express arithmetic with it/ (?)

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:237: But `Huge` might be useful, and we can compute
with it and use the result of that computation if the result
On 2014/08/20 00:32:10, gri wrote:
> we can compute with it: another place where you have a constant expression - a
> careful reader not familiar with Go might wonder where this computation
happens
> - before you said there's not much that can be done with constants

Acknowledged.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:245: In a related way, floating-point constants may
have very high precision, so that calculations involving them are more accurate.
On 2014/08/20 00:32:10, gri wrote:
> so that arithmetic involving them is more accurate.

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:261: soft underflows, and `NaNs` to arise in constant
expressions.
On 2014/08/20 00:32:10, gri wrote:
> s/to // (?)

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:289: prints `complex128:` `(2+0i)`.
On 2014/08/20 01:30:38, adg wrote:
> this fragment doesn't follow from the previous sentence

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:302: They have more moving parts—many sizes, signed or
unsigned, and more—but they play by the same rules.
On 2014/08/20 01:30:38, adg wrote:
> maybe another place to link the numbers section of the spec

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:336: .play -edit constants/int3.go /var/
On 2014/08/20 01:30:39, adg wrote:
> show a large number assignment, too?

that was done immediately above.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:346: Here is an informative little exercise
On 2014/08/20 00:32:10, gri wrote:
> missing : at end

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:348: The number of bits available depends on the
architecture, so we can't just write down a single value.
On 2014/08/20 01:30:38, adg wrote:
> this sentence should be part of the text after the MaxUint32 decl

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:355: Fans of 2's-complement arithmetic, which Go's
integers are defined to use, know that the representation of `-1` has all its
bits set to 1, so the bit pattern of `-1` is internally the same as that of the
On 2014/08/20 01:30:39, adg wrote:
> link to http://en.wikipedia.org/wiki/Two ?

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:361: but that is illegal because the abstract number
-1 cannot be represented by an unsigned variable; `-1` is not in the range of
unsigned values.
On 2014/08/20 00:32:10, gri wrote:
> s/abstract // (?)

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:366: Even though at run-time a value of -1 can be
converted to an unsigned integer, the rules of constants forbid this kind of
coercion at compile time.
On 2014/08/20 00:32:10, gri wrote:
> s/of constants/for constant conversions/

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:382: The solution is to tell Go how many bits to use
to represent the `0`, and invert that.
i don't think your version explains it very well and has its own issues. ^0 is
not a negative number, for example.
i've taken another crack at it. see if you like it better.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:393: Whatever the number of bits it takes to represent
a `uint` in the current execution environment (on the playground, it's 32),
On 2014/08/20 01:30:39, adg wrote:
> link to //blog.golang.org/playground

Done.

https://codereview.appspot.com/125540043/diff/20001/content/constants.article...
content/constants.article:404: All these constants have numeric value 1
On 2014/08/20 00:32:10, gri wrote:
> missing : at end ?

Done.

[r, 2014-08-20 17:54:21]

Hello gri@golang.org, adg@golang.org (cc: golang-codereviews@googlegroups.com),

I'd like you to review this change to
https://code.google.com/p/go.blog

[gri, 2014-08-20 17:58:06]

LGTM

https://codereview.appspot.com/125540043/diff/40001/content/constants.article
File content/constants.article (right):

https://codereview.appspot.com/125540043/diff/40001/content/constants.article...
content/constants.article:381: But that fails too, for a similar reason: ^0
represents an infinite number of 1s, and we lose information if we assign that
to any fixed-size integer:
perhaps, to make that a bit more obvious:

s/: ^0/: In the ideal space of numeric values, ^0/

[adg, 2014-08-21 03:24:16]

LGTM

https://codereview.appspot.com/125540043/diff/80001/content/constants.article
File content/constants.article (right):

https://codereview.appspot.com/125540043/diff/80001/content/constants.article...
content/constants.article:2: 19 Aug 2014
Shall we post it on the 25th? (Monday)

[r, 2014-08-21 04:27:32]

SGTM. You'll do the submitting and posting, right?

On Wed, Aug 20, 2014 at 8:24 PM,  <adg@golang.org> wrote:
> LGTM
>
>
> https://codereview.appspot.com/125540043/diff/80001/content/constants.article
> File content/constants.article (right):
>
>
https://codereview.appspot.com/125540043/diff/80001/content/constants.article...
> content/constants.article:2: 19 Aug 2014
> Shall we post it on the 25th? (Monday)
>
> https://codereview.appspot.com/125540043/

[rsc, 2014-08-22 00:39:36]

LGTM

https://codereview.appspot.com/125540043/diff/80001/content/constants.article
File content/constants.article (right):

https://codereview.appspot.com/125540043/diff/80001/content/constants.article...
content/constants.article:194: Integer constants default to `int`,
floating-point constants `float64`, rune constants to `rune` (an alias for
`int32`), imaginary constants to `complex128`, and so on.
I don't think there's an "and so on". That's all the options.

https://codereview.appspot.com/125540043/diff/80001/content/constants.article...
content/constants.article:442: const milliSecond = time.Second/1e3
s/milliSecond/millisecond/.
caps are for the beginning of a new word. millisecond is one word.

[r, 2014-08-22 18:51:13]

https://codereview.appspot.com/125540043/diff/80001/content/constants.article
File content/constants.article (right):

https://codereview.appspot.com/125540043/diff/80001/content/constants.article...
content/constants.article:194: Integer constants default to `int`,
floating-point constants `float64`, rune constants to `rune` (an alias for
`int32`), imaginary constants to `complex128`, and so on.
On 2014/08/22 00:39:36, rsc wrote:
> I don't think there's an "and so on". That's all the options.

Done.

https://codereview.appspot.com/125540043/diff/80001/content/constants.article...
content/constants.article:442: const milliSecond = time.Second/1e3
On 2014/08/22 00:39:36, rsc wrote:
> s/milliSecond/millisecond/.
> caps are for the beginning of a new word. millisecond is one word.

Done.

[adg, 2014-08-25 01:44:08]

*** Submitted as
https://code.google.com/p/go/source/detail?r=0362e1feb038&repo=blog ***

go.blog: constants

LGTM=gri, adg, rsc
R=gri, adg, rsc
CC=golang-codereviews
https://codereview.appspot.com/125540043

Committer: Andrew Gerrand <adg@golang.org>