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Editorial Team
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Asked: 2026-05-26T16:51:45+00:00

Ruby on Rails has the method String#starts_with? , which is implemented in Ruby with

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Ruby on Rails has the method String#starts_with?, which is implemented in Ruby with

# File lib/active_support/core_ext/string/starts_ends_with.rb, line 22
def starts_with?(prefix)
  prefix = prefix.to_s
  self[0, prefix.length] == prefix
end

whereas Ruby, since version 1.8.7, has the method String#start_with?, which is implemented in C

static VALUE
rb_str_start_with(int argc, VALUE *argv, VALUE str)
{
    int i;

    for (i=0; i<argc; i++) {
        VALUE tmp = rb_check_string_type(argv[i]);
        if (NIL_P(tmp)) continue;
        rb_enc_check(str, tmp);
        if (RSTRING_LEN(str) < RSTRING_LEN(tmp)) continue;
        if (memcmp(RSTRING_PTR(str), RSTRING_PTR(tmp), RSTRING_LEN(tmp)) == 0)
            return Qtrue;
    }
    return Qfalse;
}

Why don’t they just have an alias linking from starts_with? to start_with??

Do they wish to maintain compatibility with Ruby 1.8.6, or are they worried that start_with? may have different behavior to starts_with?, or have they not seen the need to update the code?

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1 Answer

  1. Editorial Team

    From your code, it looks like you have a really old version of Rails at hand (<= 2.3.5). As this version supported older Ruby versions, which didn’t yet had start_with? they implemented it by hand.

    However if you look above in the file, you see that they used the ruby built-in method if it is available. In newer Rails versions where the Ruby 1.8.6 support was dropped, these magic bits were removed and ActiveSupport now provides unconditional aliases.

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