Source files

Overview

A Carbon source file is a sequence of Unicode code points in Unicode Normalization Form C ("NFC"), and represents a portion of the complete text of a program.

Program text can come from a variety of sources, such as an interactive programming environment (a so-called "Read-Evaluate-Print-Loop" or REPL), a database, a memory buffer of an IDE, or a command-line argument.

The canonical representation for Carbon programs is in files stored as a sequence of bytes in a file system on disk. Such files have a .carbon extension.

Encoding

The on-disk representation of a Carbon source file is encoded in UTF-8. Such files may begin with an optional UTF-8 BOM, that is, the byte sequence EF₁₆,BB₁₆,BF₁₆. This prefix, if present, is ignored.

No Unicode normalization is performed when reading an on-disk representation of a Carbon source file, so the byte representation is required to be normalized in Normalization Form C. The Carbon source formatting tool will convert source files to NFC as necessary.

Alternatives considered

• Character encoding
• Byte order marks
• Normalization forms

References

• Proposal #142: Unicode source files

• Unicode is a universal character encoding, maintained by the Unicode Consortium. It is the canonical encoding used for textual information interchange across all modern technology.

  Carbon is based on Unicode 13.0, which is currently the latest version of the Unicode standard. Newer versions will be considered for adoption as they are released.

• Unicode Standard Annex #15: Unicode Normalization Forms

• Wikipedia Unicode equivalence page: Normal forms