Kotlin with in Julia

with.jl

function changeSymbol(target, to, expr)
    function dfs(expr)
        args = expr.args
        for i in 1:length(args)
            arg = args[i]
            if arg isa Expr
                dfs(arg)
            elseif arg isa Symbol
                if arg == target
                    args[i] = to
                end
            end
        end
    end
    dfs(expr)
    expr
end

macro with(var, expr)
    symbols = fieldnames(typeof(eval(var)))
    for symbol in symbols
        changeSymbol(symbol, :($var.$symbol), expr)
    end
    expr
end

mutable struct Foo
    x::Int
    y::String
end

foo = Foo(42, "meow")

macroexpand(Main, :(@with foo begin
    x = 1
    y = "2"
end))

@with foo begin
    x = 1
    y = "2"
end

println(foo)

withV2.jl

function changeSymbol(target, to, expr)
    function dfs(expr)
        args = expr.args
        for i in 1:length(args)
            arg = args[i]
            if arg isa Expr
                dfs(arg)
            elseif arg isa Symbol
                if arg == target
                    args[i] = to
                end
            end
        end
    end
    dfs(expr)
    expr
end

mutable struct Foo
    x::Int
    y::String
end

function with(var, expr)
    symbols = fieldnames(typeof(var))
    for symbol in symbols
        changeSymbol(symbol, :($var.$symbol), expr)
    end
    expr
end

function boo()
    foo = Foo(42, "meow")
    println(foo)
    eval(with(foo, quote
        x = 1
        y = "2"
    end))
    println(foo)
end

boo()