mirror of
https://github.com/nim-lang/Nim.git
synced 2025-12-28 08:54:53 +00:00
77 lines
1.7 KiB
Nim
77 lines
1.7 KiB
Nim
discard """
|
|
output: "Using test.Closing test."
|
|
"""
|
|
|
|
import
|
|
macros
|
|
|
|
# This macro mimics the using statement from C#
|
|
#
|
|
# It's kept only as a test for the macro system
|
|
# Nim's destructors offer a mechanism for automatic
|
|
# disposal of resources.
|
|
#
|
|
macro autoClose(args: varargs[untyped]): untyped =
|
|
let e = callsite()
|
|
if e.len != 3:
|
|
error "Using statement: unexpected number of arguments. Got " &
|
|
$e.len & ", expected: 1 or more variable assignments and a block"
|
|
|
|
var args = e
|
|
var body = e[2]
|
|
|
|
var
|
|
variables : seq[NimNode]
|
|
closingCalls : seq[NimNode]
|
|
|
|
newSeq(variables, 0)
|
|
newSeq(closingCalls, 0)
|
|
|
|
for i in countup(1, args.len-2):
|
|
if args[i].kind == nnkExprEqExpr:
|
|
var varName = args[i][0]
|
|
var varValue = args[i][1]
|
|
|
|
var varAssignment = newNimNode(nnkIdentDefs)
|
|
varAssignment.add(varName)
|
|
varAssignment.add(newNimNode(nnkEmpty)) # empty means no type
|
|
varAssignment.add(varValue)
|
|
variables.add(varAssignment)
|
|
|
|
closingCalls.add(newCall(newIdentNode("close"), varName))
|
|
else:
|
|
error "Using statement: Unexpected expression. Got " &
|
|
$args[i].kind & " instead of assignment."
|
|
|
|
var varSection = newNimNode(nnkVarSection)
|
|
varSection.add(variables)
|
|
|
|
var finallyBlock = newNimNode(nnkStmtList)
|
|
finallyBlock.add(closingCalls)
|
|
|
|
result = quote do:
|
|
block:
|
|
`varSection`
|
|
try:
|
|
`body`
|
|
finally:
|
|
`finallyBlock`
|
|
|
|
type
|
|
TResource* = object
|
|
field*: string
|
|
|
|
proc openResource(param: string): TResource =
|
|
result.field = param
|
|
|
|
proc close(r: var TResource) =
|
|
write(stdout, "Closing " & r.field & ".")
|
|
|
|
proc use(r: var TResource) =
|
|
write(stdout, "Using " & r.field & ".")
|
|
|
|
autoClose(r = openResource("test")):
|
|
use r
|
|
|
|
write stdout, "\n"
|