Module exif::doc::upgrade

Upgrade Guide

Upgrade from 0.4.x to 0.5.x

API compatibilities

• Reader has been split into two: Reader and Exif. Reader is now the builder for Exif, and Exif provides access to Fields via get_field, fields, and other methods. Old code Reader::new(data) should be changed to Reader::new().read_raw(data) or Reader::new().read_from_container(data).

  The old code using 0.4.x:

  let reader = Reader::new(&mut bufreader).unwrap();
  for f in reader.fields() { /* do something */ }

  The new code using 0.5.x:

  let exif = Reader::new().read_from_container(&mut bufreader).unwrap();
  for f in exif.fields() { /* do something */ }

Other new features

• Support for parsing Exif in HEIF (HEIC/AVIF) has been added.

Upgrade from 0.3.x to 0.4.x

API compatibilities

• Use struct In instead of bool to indicate primary/thumbnail images.
  • On Reader::get_field, the old code using 0.3.x:

    reader.get_field(Tag::DateTime, false)

    The new code using 0.4.x:

    reader.get_field(Tag::DateTime, In::PRIMARY)

    As an additional feature, access to the 2nd or further IFD, which some TIFF-based RAW formats may have, is also possible with 0.4.x:

    reader.get_field(Tag::ImageWidth, In(2))

  • On Field, the old code using 0.3.x:

    if field.thumbnail {
        // for the thumbnail image
    } else {
        // for the primary image
    }

    The new code using 0.4.x:

    match field.ifd_num {
        In::PRIMARY => {},   // for the primary image
        In::THUMBNAIL => {}, // for the thumbnail image
        _ => {},
    }

• Reader::fields now returns an iterator instead of a slice.
• Enum variants of Context and Error are no longer exhaustive. You need a wildcard arm (_) in a match expression.
• The associated value of Value::Undefined and Value::Ascii has been changed from a slice to a Vec.

Other new features

• Field::display_value has been introduced. It is usually handier than Value::display_as.

  assert_eq!(field.display_value().to_string(),
             field.value.display_as(field.tag).to_string());

• Displaying a value with its unit is supported.

  // Display the value only.
  println!("{}", field.display_value());
  // Display the value with its unit.  If the unit depends on another
  // field, it is taken from the reader.
  println!("{}", field.display_value().with_unit(&reader));

• Value and Field are self-contained and no longer borrow the raw buffer or Reader (thanks to the change of Value::Undefined and Value::Ascii described above).