EC
Encoding::CompatibilityError
RubyERRORNotableEncoding

Encodings are incompatible for concatenation

Quick Answer

Normalise all strings to the same encoding (usually UTF-8) before combining them.

What this means

Raised when two strings with incompatible encodings are used together in an operation such as concatenation or comparison. For example, concatenating a UTF-8 string with a UTF-16 string.

Why it happens
  1. 1Concatenating strings with different incompatible encodings
  2. 2Interpolating a binary-encoded string into a UTF-8 string

Fix

Normalise to UTF-8 before combining

Normalise to UTF-8 before combining
a = "UTF-8 string"
b = "binary data".force_encoding('BINARY')
combined = a + b.encode('UTF-8', invalid: :replace, undef: :replace)

Why this works

Encoding both strings to UTF-8 makes them compatible for concatenation.

Code examples
Reproducing the errorruby
a = "hello".encode('UTF-8')
b = "world".encode('UTF-16')
a + b
# Encoding::CompatibilityError: incompatible character encodings: UTF-8 and UTF-16
Check compatibilityruby
Encoding.compatible?(a, b)   # => nil if incompatible
Normalise before concatruby
combined = a + b.encode(a.encoding)
Sources
Official documentation ↗

Ruby Core Documentation

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