This is heavy biased to C++, which is a language that already has too many features that people just want to use. This is a very specific case to be placed as a language feature, and could be just a lib.

If this becomes a C++ feature, imagine how many data structures we would need to support?

Many other languages, specially the FP languages, allow to do that as a library. Even the languages that are only inspired by FP. Example, Ruby:

  class BinTree
    include Enumerable
  
    def initialize v, l, r
      @v, @l, @r = v, l, r
    end
  
    def each &block
      @l.each(&block) unless @l.nil?
      yield @v
      @r.each(&block) unless @r.nil? 
    end
  end

Using the Enumerable mixin includes many FP-based methods, such as map, filter and reduce by only defining each, which in this case is DFS.

Then we can proceed to define a binary tree:

  tree = BinTree.new(
    1,
    BinTree.new(
      2,
      BinTree.new(4, nil, nil),
      BinTree.new(5, nil, nil)
    ),
    BinTree.new(
      3,
      BinTree.new(6, nil, nil),
      BinTree.new(7, nil, nil),
    )                 
  )

Iterate over all the elements:

  tree.each{|v| puts v}

Iterate over the even elements:

  tree.filter{|v| v.even?}.each{|v| puts v}

Stop iteration when finding a value:

  tree.each do |v|
    break if v == 1
    puts v
  end

And so on. The same can be done in Python, Kotlin and many others.