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Slicing in Nim is very similar to Python. However, they are not completely identical.
Similarities
| (1) similarities
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numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
s = "0123456789"
print(numbers[0:2]) # [0, 1]
print(s[0:2]) # 01
print(numbers[7:]) # [7, 8, 9]
print(s[7:]) # 789
print(numbers[-2:]) # [8, 9]
print(s[-2:]) # 89
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let
numbers = @[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
s = "0123456789"
echo numbers[0 ..< 2] # @[0, 1]
echo s[0 ..< 2] # 01
echo numbers[7 .. ^1] # @[7, 8, 9]
echo s[7 .. ^1] # 789
echo numbers[^2 .. ^1] # @[8, 9]
echo s[^2 .. ^1] # 89
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Differences
| (2) differences
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numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
s = "0123456789"
print(numbers[2:0]) # []
print(s[2:0]) # "" (empty string)
print(numbers[8:100]) # [8, 9]
print(s[8:100]) # "89"
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let
numbers = @[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
s = "0123456789"
# if start index > end index => error
#echo numbers[2 ..< 0] # error
#echo s[2 ..< 0] # error
# if end index > length => error
#echo numbers[8 ..< 100] # error
#echo s[8 ..< 100] # error
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Solution
We can have a Python-like behaviour with the introduction of a safety function.
| (3) solution
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numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
s = "0123456789"
print(numbers[2:0]) # []
print(s[2:0]) # "" (empty string)
print(numbers[8:100]) # [8, 9]
print(s[8:100]) # "89"
# normal call
print(numbers[2:5]) # [2, 3, 4]
print(s[2:5]) # "234"
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import std/strutils # join
proc safeSlice[T](arr: openArray[T], lo, hi: int): auto =
## Python-like (safe) slicing.
## `lo` is included, `hi` is NOT included (like in Python)
if lo >= arr.len or lo > hi:
when T is char: return ""
else: return newSeq[T]()
# else:
let stop = if hi <= arr.len: hi else: arr.len
when T is char: return arr[lo ..< stop].join
else: return arr[lo ..< stop]
let
numbers = @[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
s = "0123456789"
echo numbers.safeSlice(2, 0); # []
echo s.safeSlice(2, 0); # "" (empty string)
echo numbers.safeSlice(8, 100); # [8, 9]
echo s.safeSlice(8, 100); # "89"
# normal call
echo numbers.safeSlice(2, 5); # [2, 3, 4]
echo s.safeSlice(2, 5); # "234"
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when is a compile-time branch
auto as the return type lets Nim infer the correct type per instantiation (string or seq[T])
Links
- In D, it's the same. See here.
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