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when not defined(nimHasSystemRaisesDefect):
{.pragma: systemRaisesDefect.}
type
BackwardsIndex* = distinct int ## Type that is constructed by `^` for
## reversed array accesses.
## (See `^ template <#^.t,int>`_)
template `^`*(x: int): BackwardsIndex = BackwardsIndex(x)
## Builtin `roof`:idx: operator that can be used for convenient array access.
## `a[^x]` is a shortcut for `a[a.len-x]`.
##
## ```nim
## let
## a = [1, 3, 5, 7, 9]
## b = "abcdefgh"
##
## echo a[^1] # => 9
## echo b[^2] # => g
## ```
proc `[]`*[T](s: openArray[T]; i: BackwardsIndex): T {.inline, systemRaisesDefect.} =
system.`[]`(s, s.len - int(i))
proc `[]`*[Idx, T](a: array[Idx, T]; i: BackwardsIndex): T {.inline, systemRaisesDefect.} =
a[Idx(a.len - int(i) + int low(a))]
proc `[]`*(s: string; i: BackwardsIndex): char {.inline, systemRaisesDefect.} = s[s.len - int(i)]
proc `[]`*[T](s: var openArray[T]; i: BackwardsIndex): var T {.inline, systemRaisesDefect.} =
system.`[]`(s, s.len - int(i))
proc `[]`*[Idx, T](a: var array[Idx, T]; i: BackwardsIndex): var T {.inline, systemRaisesDefect.} =
a[Idx(a.len - int(i) + int low(a))]
proc `[]`*(s: var string; i: BackwardsIndex): var char {.inline, systemRaisesDefect.} = s[s.len - int(i)]
proc `[]=`*[T](s: var openArray[T]; i: BackwardsIndex; x: T) {.inline, systemRaisesDefect.} =
system.`[]=`(s, s.len - int(i), x)
proc `[]=`*[Idx, T](a: var array[Idx, T]; i: BackwardsIndex; x: T) {.inline, systemRaisesDefect.} =
a[Idx(a.len - int(i) + int low(a))] = x
proc `[]=`*(s: var string; i: BackwardsIndex; x: char) {.inline, systemRaisesDefect.} =
s[s.len - int(i)] = x
template `..^`*(a, b: untyped): untyped =
## A shortcut for `.. ^` to avoid the common gotcha that a space between
## '..' and '^' is required.
a .. ^b
template `..<`*(a, b: untyped): untyped =
## A shortcut for `a .. pred(b)`.
## ```nim
## for i in 5 ..< 9:
## echo i # => 5; 6; 7; 8
## ```
a .. (when b is BackwardsIndex: succ(b) else: pred(b))
template `[]`*(s: string; i: int): char = arrGet(s, i)
template `[]=`*(s: string; i: int; val: char) = arrPut(s, i, val)
template `^^`(s, i: untyped): untyped =
(when i is BackwardsIndex: s.len - int(i) else: int(i))
template spliceImpl(s, a, L, b: typed): untyped =
# make room for additional elements or cut:
var shift = b.len - max(0,L) # ignore negative slice size
var newLen = s.len + shift
if shift > 0:
# enlarge:
setLen(s, newLen)
for i in countdown(newLen-1, a+b.len): movingCopy(s[i], s[i-shift])
else:
for i in countup(a+b.len, newLen-1): movingCopy(s[i], s[i-shift])
# cut down:
setLen(s, newLen)
# fill the hole:
for i in 0 ..< b.len: s[a+i] = b[i]
proc `[]`*[T, U: Ordinal](s: string, x: HSlice[T, U]): string {.inline, systemRaisesDefect.} =
## Slice operation for strings.
## Returns the inclusive range `[s[x.a], s[x.b]]`:
## ```nim
## var s = "abcdef"
## assert s[1..3] == "bcd"
## ```
let a = s ^^ x.a
let L = (s ^^ x.b) - a + 1
result = newString(L)
for i in 0 ..< L: result[i] = s[i + a]
proc `[]=`*[T, U: Ordinal](s: var string, x: HSlice[T, U], b: string) {.systemRaisesDefect.} =
## Slice assignment for strings.
##
## If `b.len` is not exactly the number of elements that are referred to
## by `x`, a `splice`:idx: is performed:
##
runnableExamples:
var s = "abcdefgh"
s[1 .. ^2] = "xyz"
assert s == "axyzh"
var a = s ^^ x.a
var L = (s ^^ x.b) - a + 1
if L == b.len:
for i in 0..<L: s[i+a] = b[i]
else:
spliceImpl(s, a, L, b)
proc `[]`*[Idx, T; U, V: Ordinal](a: array[Idx, T], x: HSlice[U, V]): seq[T] {.systemRaisesDefect.} =
## Slice operation for arrays.
## Returns the inclusive range `[a[x.a], a[x.b]]`:
## ```nim
## var a = [1, 2, 3, 4]
## assert a[0..2] == @[1, 2, 3]
## ```
##
## See also:
## * `toOpenArray(array[I, T];I,I) <#toOpenArray,array[I,T],I,I>`_
let xa = a ^^ x.a
let L = (a ^^ x.b) - xa + 1
result = newSeq[T](L)
for i in 0..<L: result[i] = a[Idx(i + xa)]
proc `[]=`*[Idx, T; U, V: Ordinal](a: var array[Idx, T], x: HSlice[U, V], b: openArray[T]) {.systemRaisesDefect.} =
## Slice assignment for arrays.
## ```nim
## var a = [10, 20, 30, 40, 50]
## a[1..2] = @[99, 88]
## assert a == [10, 99, 88, 40, 50]
## ```
let xa = a ^^ x.a
let L = (a ^^ x.b) - xa + 1
if L == b.len:
for i in 0..<L: a[Idx(i + xa)] = b[i]
else:
sysFatal(RangeDefect, "different lengths for slice assignment")
proc `[]`*[T; U, V: Ordinal](s: openArray[T], x: HSlice[U, V]): seq[T] {.systemRaisesDefect.} =
## Slice operation for sequences.
## Returns the inclusive range `[s[x.a], s[x.b]]`:
## ```nim
## var s = @[1, 2, 3, 4]
## assert s[0..2] == @[1, 2, 3]
## ```
##
## See also:
## * `toOpenArray(openArray[T];int,int) <#toOpenArray,openArray[T],int,int>`_
let a = s ^^ x.a
let L = (s ^^ x.b) - a + 1
newSeq(result, L)
for i in 0 ..< L: result[i] = s[i + a]
proc `[]=`*[T; U, V: Ordinal](s: var seq[T], x: HSlice[U, V], b: openArray[T]) {.systemRaisesDefect.} =
## Slice assignment for sequences.
##
## If `b.len` is not exactly the number of elements that are referred to
## by `x`, a `splice`:idx: is performed.
runnableExamples:
var s = @"abcdefgh"
s[1 .. ^2] = @"xyz"
assert s == @"axyzh"
let a = s ^^ x.a
let L = (s ^^ x.b) - a + 1
if L == b.len:
for i in 0 ..< L: s[i+a] = b[i]
else:
spliceImpl(s, a, L, b)
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