Hello,
I'm trying to create range types with redefined operators but encountering some
issues.
My program writes characters to a VGA buffer that has 80 columns and 25 lines.
I figured I'd write range types for the columns and lines which I named
VGACursor and VGALine respectively, and redefine the += operator so that they
wrap around (go back to their low value when superior to their high value).
Here is the code in question:
type
VGABuffer* = ptr array[0..2000, uint16]
VGALine* = distinct range[0..24]
VGACursor* = distinct range[0..79]
FILE = object
var
line: VGALine = 0.VGALine
cursor: VGACursor = 0.VGACursor
proc `+=` (a: VGALine, b: int): VGALine = return ((a.int+b) mod 80).VGALine
proc `+=` (a: VGACursor, b: int): VGACursor =
if (a.int+b) > 25:
line += 1
return ((a.int+b) mod 25).VGACursor
var stdout* {.exportc.} : ptr FILE
var stderr* {.exportc.} : ptr FILE
const video_memory = cast[VGABuffer](0xB8000)
proc flockfile(f: ptr FILE) {.exportc.} = discard
proc funlockfile(f: ptr FILE) {.exportc.} = discard
proc fflush(stream: ptr FILE): cint {.exportc.} = 0.cint
proc fwrite(data: cstring, size: csize_t, nitems: csize_t, stream: ptr
FILE): csize_t {.exportc.} =
let
backColour: byte = 0b00000000
foreColour: byte = 0b00001111
colour: byte = (backColour shl 4) or foreColour
for i in 0..<size:
var
c = data[i]
info = c.uint8 or (colour.uint16 shl 8)
if c == '\n':
line += 1
else:
cursor += 1
video_memory[cursor.int+(line.int*80)] = info
line += 1
return nitems
Run
And I get the error: `stdio.nim(16, 10) Error: expression 'line += 1' is of
type 'VGALine' and has to be used (or discarded)`
I don't know what that means, or why it appears since I've declared unused
variables with no issues in the past.
Could you help me understand? Also could you tell me if this is the idiomatic
solution for creating wrapping range types?
