String#<<

(::string | ::Integer str_or_codepoint) -> self

string << object → string

VALUE
rb_str_concat(VALUE str1, VALUE str2)
{
    unsigned int code;
    rb_encoding *enc = STR_ENC_GET(str1);
    int encidx;

    if (RB_INTEGER_TYPE_P(str2)) {
        if (rb_num_to_uint(str2, &code) == 0) {
        }
        else if (FIXNUM_P(str2)) {
            rb_raise(rb_eRangeError, "%ld out of char range", FIX2LONG(str2));
        }
        else {
            rb_raise(rb_eRangeError, "bignum out of char range");
        }
    }
    else {
        return rb_str_append(str1, str2);
    }

    encidx = rb_ascii8bit_appendable_encoding_index(enc, code);

    if (encidx >= 0) {
        rb_str_buf_cat_byte(str1, (unsigned char)code);
    }
    else {
        long pos = RSTRING_LEN(str1);
        int cr = ENC_CODERANGE(str1);
        int len;
        char *buf;

        switch (len = rb_enc_codelen(code, enc)) {
          case ONIGERR_INVALID_CODE_POINT_VALUE:
            rb_raise(rb_eRangeError, "invalid codepoint 0x%X in %s", code, rb_enc_name(enc));
            break;
          case ONIGERR_TOO_BIG_WIDE_CHAR_VALUE:
          case 0:
            rb_raise(rb_eRangeError, "%u out of char range", code);
            break;
        }
        buf = ALLOCA_N(char, len + 1);
        rb_enc_mbcput(code, buf, enc);
        if (rb_enc_precise_mbclen(buf, buf + len + 1, enc) != len) {
            rb_raise(rb_eRangeError, "invalid codepoint 0x%X in %s", code, rb_enc_name(enc));
        }
        rb_str_resize(str1, pos+len);
        memcpy(RSTRING_PTR(str1) + pos, buf, len);
        if (cr == ENC_CODERANGE_7BIT && code > 127) {
            cr = ENC_CODERANGE_VALID;
        }
        else if (cr == ENC_CODERANGE_BROKEN) {
            cr = ENC_CODERANGE_UNKNOWN;
        }
        ENC_CODERANGE_SET(str1, cr);
    }
    return str1;
}

Concatenates object to self and returns self:

Example

s = 'foo'
s << 'bar' # => "foobar"
s          # => "foobar"

If object is an Integer, the value is considered a codepoint and converted to a character before concatenation:

Example

s = 'foo'
s << 33 # => "foo!"

If that codepoint is not representable in the encoding of string, RangeError is raised.

Example

s = 'foo'
s.encoding              # => <Encoding:UTF-8>
s << 0x00110000         # 1114112 out of char range (RangeError)
s = 'foo'.encode('EUC-JP')
s << 0x00800080         # invalid codepoint 0x800080 in EUC-JP (RangeError)

If the encoding is US-ASCII and the codepoint is 0..0xff, string is automatically promoted to ASCII-8BIT.

Example

s = 'foo'.encode('US-ASCII')
s << 0xff
s.encoding              # => #<Encoding:BINARY (ASCII-8BIT)>

Related: String#concat, which takes multiple arguments.

See also #-@ #<=> #+@ #== also in 4.1 · 4.0 · 3.3 · 3.2 · 3.1 · 3.0

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