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Better errors when using a proc without a return type in a .? chain

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This commit is contained in:
Mark Spanbroek 2021-08-30 15:58:29 +02:00
parent b9a090d001
commit 4967084d22
1 changed files with 12 additions and 3 deletions
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15
questionable/chaining.nim
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@ -1,5 +1,6 @@
import std/options import std/options
import std/macros import std/macros
import std/strformat
func isSym(node: NimNode): bool = func isSym(node: NimNode): bool =
node.kind in {nnkSym, nnkOpenSymChoice, nnkClosedSymChoice} node.kind in {nnkSym, nnkOpenSymChoice, nnkClosedSymChoice}
@ -7,14 +8,20 @@ func isSym(node: NimNode): bool =
func expectSym(node: NimNode) = func expectSym(node: NimNode) =
node.expectKind({nnkSym, nnkOpenSymChoice, nnkClosedSymChoice}) node.expectKind({nnkSym, nnkOpenSymChoice, nnkClosedSymChoice})
macro expectReturnType(identifier: untyped, expression: untyped): untyped =
let message =
fmt"'{identifier}' doesn't have a return type, it can't be in a .? chain"
quote do:
when compiles(`expression`) and not compiles(typeof `expression`):
{.error: `message`.}
template `.?`*(option: typed, identifier: untyped{nkIdent}): untyped = template `.?`*(option: typed, identifier: untyped{nkIdent}): untyped =
## The `.?` chaining operator is used to safely access fields and call procs ## The `.?` chaining operator is used to safely access fields and call procs
## on Options or Results. The expression is only evaluated when the preceding ## on Options or Results. The expression is only evaluated when the preceding
## Option or Result has a value. ## Option or Result has a value.
# chain is of shape: option.?identifier # chain is of shape: option.?identifier
when not compiles(typeof(option.unsafeGet.identifier)): expectReturnType(identifier, option.unsafeGet.identifier)
{.error: ".? chain cannot return void".}
option ->? option.unsafeGet.identifier option ->? option.unsafeGet.identifier
macro `.?`*(option: typed, infix: untyped{nkInfix}): untyped = macro `.?`*(option: typed, infix: untyped{nkInfix}): untyped =
@ -70,7 +77,9 @@ macro `.?`*(option: typed, call: untyped{nkCall}): untyped =
else: else:
# chain is of shape: option.?procedure(arguments) # chain is of shape: option.?procedure(arguments)
call.insert(1, quote do: `option`.unsafeGet) call.insert(1, quote do: `option`.unsafeGet)
quote do: `option` ->? `call` quote do:
expectReturnType(`procedure`, `call`)
`option` ->? `call`
macro `.?`*(option: typed, symbol: untyped): untyped = macro `.?`*(option: typed, symbol: untyped): untyped =
## The `.?` chaining operator is used to safely access fields and call procs ## The `.?` chaining operator is used to safely access fields and call procs