diman_unit_system 0.4.0

Internal procedural macros for diman.
Documentation 
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use proc_macro2::TokenStream;
use quote::{format_ident, quote, quote_spanned};
use syn::Type;

use crate::{
    storage_types::{FloatType, VectorType},
    types::{Defs, Unit},
};

impl Defs {
    pub fn unit_constructors(&self) -> TokenStream {
        self.units
            .iter()
            .map(|unit| {
                let dimension = self.get_dimension_expr(&unit.dimensions);
                let vector_impls: TokenStream = self
                    .vector_types()
                    .iter()
                    .map(|vector_type| self.vector_unit_constructor(vector_type, unit, &dimension))
                    .collect();
                let float_impls: TokenStream = self
                    .float_types()
                    .iter()
                    .map(|float_type| self.float_unit_constructor(float_type, unit, &dimension))
                    .collect();
                let conversion_impls: TokenStream = self
                    .storage_types_with_base_names()
                    .into_iter()
                    .map(|(storage_type, float_type)| {
                        self.conversion_impls(storage_type, float_type, unit, &dimension)
                    })
                    .collect();
                quote! {
                    #conversion_impls
                    #float_impls
                    #vector_impls
                }
            })
            .collect()
    }

    fn conversion_impls(
        &self,
        storage_type: Type,
        base_type: FloatType,
        unit: &Unit,
        dimension: &TokenStream,
    ) -> TokenStream {
        let quantity_type = &self.quantity_type;
        let unit_name = &unit.name;
        let conversion_method_name = format_ident!("in_{}", unit_name);
        let factor = unit.factor;
        let base_type = &base_type.name;
        quote! {
            impl #quantity_type<#storage_type, {#dimension}> {
                pub fn #conversion_method_name(self) -> #storage_type {
                    let factor: #base_type = #factor as #base_type;
                    self.0 / factor
                }
            }
        }
    }

    fn float_unit_constructor(
        &self,
        float_type: &FloatType,
        unit: &Unit,
        quantity_dimension: &TokenStream,
    ) -> TokenStream {
        let Defs { quantity_type, .. } = &self;
        let Unit {
            name: unit_name,
            factor,
            ..
        } = unit;
        let name = &float_type.name;
        let span = self.dimension_type.span();
        // Without const_fn_floating_point_arithmetic (https://github.com/rust-lang/rust/issues/57241)
        // we cannot make unit constructors a const fn in general (since it requires the unstable
        // const_fn_floating_point_arithmetic feature). The following allows the constructor with 1.0
        // conversion factor to be const.
        let const_fn = *factor == 1.0;
        let fn_def = if const_fn {
            quote! { const fn }
        } else {
            quote! { fn }
        };
        let value = if const_fn {
            quote! { val }
        } else {
            quote! { val * #factor as #name }
        };
        quote_spanned! {span =>
            impl #quantity_type<#name, {#quantity_dimension}> {
                pub #fn_def #unit_name(val: #name) -> #quantity_type<#name, {#quantity_dimension}> {
                    #quantity_type::<#name, {#quantity_dimension}>(#value)
                }
            }
        }
    }

    fn vector_unit_constructor(
        &self,
        vector_type: &VectorType,
        unit: &Unit,
        quantity_dimension: &TokenStream,
    ) -> TokenStream {
        let Defs { quantity_type, .. } = &self;
        let Unit {
            name: unit_name,
            factor,
            ..
        } = unit;
        let VectorType {
            name,
            float_type,
            num_dims,
            ..
        } = &vector_type;
        let float_type = &float_type.name;
        let fn_args = match num_dims {
            2 => quote! { x: #float_type, y: #float_type },
            3 => quote! { x: #float_type, y: #float_type, z: #float_type },
            _ => unreachable!(),
        };
        let call_args = match num_dims {
            2 => quote! { x, y },
            3 => quote! { x, y, z },
            _ => unreachable!(),
        };
        let span = self.dimension_type.span();
        quote_spanned! {span =>
            impl #quantity_type<#name, {#quantity_dimension}> {
                pub fn #unit_name(#fn_args) -> #quantity_type<#name, {#quantity_dimension}> {
                    #quantity_type::<#name, {#quantity_dimension}>(#name::new(#call_args) * (#factor as #float_type))
                }
            }
        }
    }
}