Array.AppendAll() should have start and count arguments

bgrommes

I have an 8K buffer where I want to transfer the head of the buffer to another Array(Of Integer):

_rowChars = AppendAll(_lineBuffer,0,pos)

... but AppendAll() doesn't have this overload.

I can of course manually do this but this kind of operation would be much faster inside the VM.

My other option, which might actually even be a good one, is to use _rowChars (a weak proxy for the char[] array internally backing a string named _row) as the buffer, reserving way more space than I need. I will probably go that route, but I still think AppendAll() should be more flexible.

ETA: In this particular case I worked around it with a computed property that lazy-initializes the target array from the string itself on first access. But I still can see needing this at times.

Garry

Good suggestion.

Array.AppendAll now supports startIndex and count arguments: https://feedback.objo.dev/feature/1138

Array.AppendAll gains two range-selecting overloads alongside the existing whole-array form:

AppendAll(items As Array(Of T))
AppendAll(items As Array(Of T), startIndex As Integer)
AppendAll(items As Array(Of T), startIndex As Integer, count As Integer)

What each form does

Whole array — unchanged existing behaviour:

Var values() As Integer = [1, 2]
values.AppendAll([3, 4])
# values = [1, 2, 3, 4]

From a start index to the end of the source:

Var values() As Integer = [1]
Var extra() As Integer = [10, 20, 30, 40]
values.AppendAll(extra, 2)
# values = [1, 30, 40]

An exact half-open range [startIndex, startIndex + count):

Var values() As Integer = [1, 2]
Var extra() As Integer = [10, 20, 30, 40]
values.AppendAll(extra, 1, 2)
# values = [1, 2, 20, 30]

Notes

The methods mutate the receiver, return Void, and preserve the source elements' order.
startIndex may equal the source Count, and count may be 0 — both are valid no-ops.
A negative startIndex, a startIndex greater than the source Count, a negative count, or a range extending beyond the source raises a runtime error (IndexOutOfRangeException, or InvalidArgumentException for a negative count). The whole range is validated before the receiver is touched, so an invalid range leaves the receiver unchanged.

Self-append works with ranges too: the selected range is snapshotted first, so

  Var values() As Integer = [1, 2, 3, 4]
  values.AppendAll(values, 1, 2)
  # values = [1, 2, 3, 4, 2, 3]

Elements are appended by reference (shallow copy) exactly as before, so no deep copy, no flattening of nested arrays.