Initial proof of concept

generate-quantity/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "generate-quantity"
+description = "Macros for generating physical quantity type"
+version.workspace = true
+edition.workspace = true
+repository.workspace = true
+readme.workspace = true
+license.workspace = true
+
+[lib]
+proc-macro = true
+
+[dependencies.quote]
+workspace = true
+[dependencies.syn]
+workspace = true
+[dependencies.proc-macro2]
+workspace = true

generate-quantity/src/lib.rs

@@ -0,0 +1,143 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+use proc_macro2::{Span, TokenStream as TokenStream2};
+use quote::quote;
+use std::ops::Deref;
+use syn::parse::{Parse, ParseStream};
+use syn::{parse_macro_input, Ident, LitStr, Token};
+
+const NUMBER_TYPES: &[&str] = &[
+    "u8", "i8", "u16", "i16", "u32", "i32", "u64", "i64", "u128", "i128", "usize", "isize", "f32",
+    "f64",
+];
+
+// Define the input structure for the macro
+struct QuantityInput {
+    struct_name: Ident,
+    symbol: LitStr,
+}
+
+// Implement the parsing for the input structure
+impl Parse for QuantityInput {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let struct_name: Ident = input.parse()?;
+        input.parse::<Token![,]>()?;
+        let symbol: LitStr = input.parse()?;
+        Ok(QuantityInput {
+            struct_name,
+            symbol,
+        })
+    }
+}
+
+//TODO: Remove requirement for physical::quantity::{Quantity, Value}
+/// The following imports must be in scope for this macro to work
+/// ```
+/// use generate_quantity::quantity_type;
+/// use physical::quantity::{Quantity, Value};
+/// ```
+#[proc_macro]
+pub fn quantity_type(input: TokenStream) -> TokenStream {
+    // Parse the input tokens into the QuantityInput structure
+    let QuantityInput {
+        struct_name,
+        symbol,
+    } = parse_macro_input!(input as QuantityInput);
+
+    //----- Value Extension ----------------------------------
+    let mut val_ext_name = String::new();
+    let struct_name_str = struct_name.to_string();
+    let mut struct_name_chars = struct_name_str.chars();
+    let first = struct_name_chars
+        .next()
+        .expect("Struct name cannot be 0 length");
+    val_ext_name.push(first.to_ascii_lowercase());
+    for character in struct_name_chars {
+        if character.is_uppercase() {
+            val_ext_name.push('_');
+            val_ext_name.push(character.to_ascii_lowercase());
+        } else {
+            val_ext_name.push(character);
+        }
+    }
+    let val_ext_fn_name = Ident::new(val_ext_name.deref(), struct_name.span());
+    let val_ext_trait_name =
+        Ident::new(format!("{struct_name_str}Val").deref(), struct_name.span());
+
+    //----- Conversion impls ----------------------------------
+    let mut conversion_impls: Vec<TokenStream2> = Vec::new();
+    for &current_type in NUMBER_TYPES {
+        // Generate conversion methods for all primitive types except the current_type
+        let conversions = NUMBER_TYPES
+            .iter()
+            .filter(|&&t| t != current_type)
+            .map(|&target_type| {
+                let method_name = Ident::new(&format!("as_{}", target_type), Span::call_site());
+                let target_type = Ident::new(target_type, Span::call_site());
+
+                quote! {
+                    /// Directly [as] cast this quantities value while maintaining the type of the quantity.
+                    #[inline(always)]
+                    pub fn #method_name(self) -> #struct_name<#target_type> {
+                        #struct_name(self.0 as #target_type)
+                    }
+                }
+            })
+            .collect::<Vec<TokenStream2>>();
+
+        let current_type = Ident::new(current_type, Span::call_site());
+        // Generate the impl block for the struct with the current_type
+        let expanded = quote! {
+            impl #struct_name<#current_type> {
+                #(#conversions)*
+            }
+        };
+
+        conversion_impls.push(expanded);
+    }
+
+    //----- Output Code ----------------------------------
+    let expanded = quote! {
+        #[derive(
+            Copy,
+            Clone,
+            PartialEq,
+            PartialOrd,
+            Debug,
+            derive_more::Add,
+            derive_more::AddAssign,
+            derive_more::Sub,
+            derive_more::SubAssign,
+            derive_more::Display
+        )]
+        #[display(fmt = "{} {}", _0, "Self::symbol()")]
+        #[repr(transparent)]
+        pub struct #struct_name<V: Value>(pub V);
+
+        impl<V: Value> Quantity<V> for #struct_name<V> {
+            #[inline(always)]
+            fn value(self) -> V {
+                self.0
+            }
+
+            #[inline(always)]
+            fn symbol() -> &'static str {
+                #symbol
+            }
+        }
+
+        pub trait #val_ext_trait_name : Value {
+            /// Create a quantity in the given unit from this [Value]
+            #[inline(always)]
+            fn #val_ext_fn_name(self) -> #struct_name<Self> {
+                #struct_name(self)
+            }
+        }
+
+        impl <V: Value> #val_ext_trait_name for V {}
+
+        #(#conversion_impls)*
+    };
+
+    expanded.into()
+}