pack_bools: an easy way to pack all bools in your struct

pack_bools transforms structs with boolean fields into a struct containing an integer with bit flags for each boolean value:

use pack_bools::pack_bools;

#[pack_bools]
#[derive(Debug, Clone)]
struct Config<'a> {
    output_name: &'a str,
    verbose: bool,
    pub use_colors: bool,
    original_file: &'a std::path::Path,
    legacy_mode: bool
}

gets transformed into something like this:

#[derive(Debug, Clone)]
struct Config<'a> {
    output_name: &'a str,
    original_file: &'a std::path::Path,
    packed_bools: u8
}

impl<'a> Config<'a> {
    fn get_verbose(&self) -> bool {
        self.packed_bools & 1 << 0 != 0
    }

    fn set_verbose(&mut self, value: bool) {
        let val = self.packed_bools;
        self.packed_bools = if value {
            val | 1 << 0
        } else {
            val & !(1 << 1)
        };
    }

    pub fn get_use_colors(&self) -> bool {
        self.packed_bools & 1 << 0 != 0
    }

    pub fn set_use_colors(&mut self, value: bool) {
        let val = self.packed_bools;
        self.packed_bools = if value {
            val | 1 << 0
        } else {
            val & !(1 << 1)
        };
    }

    /* getters and setters for legacy_mode omitted */
}

Usage

Simply run cargo add pack_bools in your project directory, use pack_bools::pack_bools; and add the #[pack_bools] macro on top of your struct. By default, this will behave as the example above: it will replace all fields of type bool with a single numeric field packed_bools and add getters and setters for each field. By default, both the getter and setter will inherit their visibility from the field, so if the field is declared pub(super), the getters and setters will too.

There are lots of customization available, by adding options to the #[pack_bools(...)] attribute. Additionally, every boolean field can have a #[pack_bools(...)] attribute with additional options.

Global options available when using #[pack_bools(...)] on a struct:

• #[pack_bools(getters = [vis] <name>)] changes the name (and possibly visibility) of the getters. Use % as a substitution for the field name. Using #[pack_bools(getters = pub get_field_%)] will make all getters public named get_field_<field-name>. The visibility modifier is optional. Aliased as get/getter. For setters, use #[pack_bools(set/setter/setters = ...)] instead.
• #[pack_bools(no_getters)] will not generate getters (aliased as no_get/no_getter), similarly #[pack_bools(no_set/no_setter/no_setters)] will not generate setters.
• #[pack_bools(type = u16)] will use u16 as the data type for the bit flags. Available options are u8/u16/u32/ u64/u128/auto, where auto (the default option) automatically use the smallest of those types that can fit all the bools in the struct.
• #[pack_bools(field = <name>)] will set the name of the field containing the bitflags, by default packed_bools.
• #[pack_bools(inline)] will use the inline pattern for the bitflag field, i.e. create fields of the pattern packed_bools: u8. This is the default option. Compare to newtype below.
• #[pack_bools(newtype [= name])] will make a new single-valued tuple struct for holding the bitflags, similar to struct MyStructPackedBools(u8);. If a name is specified, the newtype struct will be defined with that name, otherwise PackedBools will be suffixed to the name of the struct. The example at the top of this document, with #[pack_bools(newtype)] will be compiled into:

#[derive(Debug, Clone)]
struct Config<'a> {
    output_name: &'a str,
    original_file: &'a Path,
    packed_bools: ConfigPackedBools
}

#[derive(Copy, Clone, Debug)]
#[repr(transparent)]
struct ConfigPackedBools(u8);

impl<'a> Config<'a> {
    fn get_verbose(&self) -> bool {
        self.packed_bools.0 & 1 << 0 != 0
    }

    fn set_verbose(&mut self, value: bool) {
        let val = self.packed_bools.0;
        self.packed_bools.0 = if value {
            val | 1 << 0
        } else {
            val & !(1 << 1)
        };
    }

    /* additional getters and setters omitted */
}

You may add the #[pack_bools(...)] attribute on fields of type bool to configure the output of that specific field. Available options are:

• #[pack_bools(skip)] excludes that field from being packed with the other bools.
• #[pack_bools(getter = [vis] <name>) changes the name (and possibly visibility) of the getter to that field. #[pack_bools(getter = pub debug_mode)] added to a field debug: bool will create a getter like pub fn debug_mode(&self) -> bool { ... }. Aliased as get. For setters, use #[pack_bools(set/setter = [vis] <name>)].
• #[pack_bools(no_getter)] skips generating a getter for that field. Aliased as no_get. For setters, use #[pack_bools(no_set/no_setter)].
• #[pack_bools(default = <true/false>)] sets the default value for the field. If set to true, the newtype pattern must be used, but then a impl Default will be generated for that newtype with this field set to true. If all other fields of the struct has appropriate default values, this will allow you to use #[derive(Default)] on the struct, while having some boolean values set to true. Defaults to false.