Referencing and Dereferencing in Nim

Here is an executable guide to how referencing and dereferencing work in Nim. I made this to understand it myself, because there is no explanation in the online manual or either book on Nim.

******************

type

refInt = ref int

var

a: int = 1

b: refInt

c: refInt

d: refInt

# UPDATE

# Use this template to make referencing much easier!

template `-->` [T](receiver: ref T, target: T)=

receiver = cast[ref type(target)](target.addr)

echo a

echo "a ", a.addr.repr

# Sadly, the Nim 2.0.0 update removed the physical addresses from repr

new(b)

b[] = a

echo b[]

echo "b ", b.addr.repr

a = 2

echo a

echo "a ", a.addr.repr

echo b[]

b = cast[ref int](alloc0(sizeOf(a))) # primitive, use new(b) instead

b[] = a

echo b[]

echo "b ", b.addr.repr

a = 3

echo a

echo b[]

b = cast[ref int](a.addr) # this works!

echo b[]

new(c)

c = b

echo "c ", c[]

a = 4

echo "a ", a

echo b[]

echo c[]

echo type(c)

echo "a ", a.addr.repr

echo "b ", b.addr.repr

echo "c ", c.addr.repr

echo ""

var x: array[5, int]

type ArrRef = ref array[5, int]

var y, z : ArrRef

x = [1, 2, 3, 4, 5]

y = cast[ArrRef](x.addr)

# addr provides a ptr type

# cast to convert ptr to ref

z = y

echo "x ", x, " is ", x.addr.repr

# repr is a lower-level version of the $ to-string operator

echo "y ", y[], " is ", y.addr.repr

# [] is dereference, so c[] --> b

echo "z ", z[], " is ", z.addr.repr

echo ""

z[4] = 10

echo "x ", x, " is ", x.addr.repr

echo "y ", y[], " is ", y.addr.repr

echo "z ", z[], " is ", z.addr.repr

new(z)

# use new() to allocate space for the value to be referenced

z[] = x

z[4] = 20

echo ""

echo "x ", x, " is ", x.addr.repr

echo "y ", y[], " is ", y.addr.repr

echo "z ", z[], " is ", z.addr.repr

# only z is now [1, 2, 3, 4, 20]

var q: ArrRef

q --> x