How to read a certain number of characters (as opposed to bytes) in Crystal?

In Crystal, if I have a string (or a file), how do I read a certain number of characters at a time? Using functions like IO#read, IO#gets, IO#read_string, and IO#read_utf8, one can specify a certain number of bytes to read, but not a certain number of UTF-8 characters (or ones of another encoding).

In Python, for example, one might do this:

from io import StringIO

s = StringIO("abcdefgh")
while True:
    chunk = s.read(4)
    if not chunk: break

Or, in the case of a file, this:

with open("example.txt", 'r') as f:
    while True:
        chunk = f.read(4)
        if not chunk: break

Generally, I'd expect IO::Memory to be the class to use for the string case, but as far as I can tell, its methods don't allow for this. How would one do this in an efficient and idiomatic fashion (for both strings and files – perhaps the answer is different for each) in Crystal?

Solution

There currently is no short cut implementation for this available in Crystal.

You can read individual chars with IO#read_char or consecutive ones with IO#each_char.

So a basic implementation would be:

io = IO::Memory.new("€abcdefgh") 

string = String.build(4) do |builder|
  4.times do
    builder << io.read_char
  end
end

puts string

Whether you use a memory IO or a file or any other IO is irrelevant, the behaviour is all the same.