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import macros
macro class*(head, body: untyped): untyped =
# The macro is immediate, since all its parameters are untyped.
# This means, it doesn't resolve identifiers passed to it.
var typeName, baseName: NimNode
# flag if object should be exported
var exported: bool
if head.kind == nnkInfix and head[0].ident == !"of":
# `head` is expression `typeName of baseClass`
# echo head.treeRepr
# --------------------
# Infix
# Ident !"of"
# Ident !"Animal"
# Ident !"RootObj"
typeName = head[1]
baseName = head[2]
elif head.kind == nnkInfix and head[0].ident == !"*" and
head[2].kind == nnkPrefix and head[2][0].ident == !"of":
# `head` is expression `typeName* of baseClass`
# echo head.treeRepr
# --------------------
# Infix
# Ident !"*"
# Ident !"Animal"
# Prefix
# Ident !"of"
# Ident !"RootObj"
typeName = head[1]
baseName = head[2][1]
exported = true
else:
quit "Invalid node: " & head.lispRepr
# The following prints out the AST structure:
#
# import macros
# dumptree:
# type X = ref object of Y
# z: int
# --------------------
# StmtList
# TypeSection
# TypeDef
# Ident !"X"
# Empty
# RefTy
# ObjectTy
# Empty
# OfInherit
# Ident !"Y"
# RecList
# IdentDefs
# Ident !"z"
# Ident !"int"
# Empty
# create a type section in the result
result =
if exported:
# mark `typeName` with an asterisk
quote do:
type `typeName`* = ref object of `baseName`
else:
quote do:
type `typeName` = ref object of `baseName`
# echo treeRepr(body)
# --------------------
# StmtList
# VarSection
# IdentDefs
# Ident !"name"
# Ident !"string"
# Empty
# IdentDefs
# Ident !"age"
# Ident !"int"
# Empty
# MethodDef
# Ident !"vocalize"
# Empty
# Empty
# FormalParams
# Ident !"string"
# Empty
# Empty
# StmtList
# StrLit ...
# MethodDef
# Ident !"age_human_yrs"
# Empty
# Empty
# FormalParams
# Ident !"int"
# Empty
# Empty
# StmtList
# DotExpr
# Ident !"this"
# Ident !"age"
# var declarations will be turned into object fields
var recList = newNimNode(nnkRecList)
# expected name of constructor
let ctorName = newIdentNode("new" & $typeName)
# Iterate over the statements, adding `this: T`
# to the parameters of functions, unless the
# function is a constructor
for node in body.children:
case node.kind:
of nnkMethodDef, nnkProcDef:
# check if it is the ctor proc
if node.name.kind != nnkAccQuoted and node.name.basename == ctorName:
# specify the return type of the ctor proc
node.params[0] = typeName
else:
# inject `self: T` into the arguments
node.params.insert(1, newIdentDefs(ident("self"), typeName))
result.add(node)
of nnkVarSection:
# variables get turned into fields of the type.
for n in node.children:
recList.add(n)
else:
result.add(node)
# Inspect the tree structure:
#
# echo result.treeRepr
# --------------------
# StmtList
# TypeSection
# TypeDef
# Ident !"Animal"
# Empty
# RefTy
# ObjectTy
# Empty
# OfInherit
# Ident !"RootObj"
# Empty <= We want to replace this
# MethodDef
# ...
result[0][0][2][0][2] = recList
# Lets inspect the human-readable version of the output
#echo repr(result)
# ---
class Animal of RootObj:
var name: string
var age: int
method vocalize: string {.base.} = "..." # use `base` pragma to annonate base methods
method age_human_yrs: int {.base.} = self.age # `this` is injected
proc `$`: string = "animal:" & self.name & ":" & $self.age
class Dog of Animal:
method vocalize: string = "woof"
method age_human_yrs: int = self.age * 7
proc `$`: string = "dog:" & self.name & ":" & $self.age
class Cat of Animal:
method vocalize: string = "meow"
proc `$`: string = "cat:" & self.name & ":" & $self.age
class Rabbit of Animal:
proc newRabbit(name: string, age: int) = # the constructor doesn't need a return type
result = Rabbit(name: name, age: age)
method vocalize: string = "meep"
proc `$`: string =
self.#[!]#
result = "rabbit:" & self.name & ":" & $self.age
# ---
var animals: seq[Animal] = @[]
animals.add(Dog(name: "Sparky", age: 10))
animals.add(Cat(name: "Mitten", age: 10))
for a in animals:
echo a.vocalize()
echo a.age_human_yrs()
let r = newRabbit("Fluffy", 3)
echo r.vocalize()
echo r.age_human_yrs()
echo r
discard """
disabled:true
$nimsuggest --tester $file
>sug $1
sug;;skField;;age;;int;;$file;;167;;6;;"";;100;;None
sug;;skField;;name;;string;;$file;;166;;6;;"";;100;;None
sug;;skMethod;;twithin_macro.age_human_yrs;;proc (self: Animal): int;;$file;;169;;9;;"";;100;;None
sug;;skMethod;;twithin_macro.vocalize;;proc (self: Animal): string;;$file;;168;;9;;"";;100;;None
sug;;skMethod;;twithin_macro.vocalize;;proc (self: Rabbit): string;;$file;;184;;9;;"";;100;;None
sug;;skMacro;;twithin_macro.class;;proc (head: untyped, body: untyped): untyped{.gcsafe, locks: <unknown>.};;$file;;4;;6;;"";;50;;None*
"""
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