Allow no_std use with Default and PhantomData

Cargo.toml

@@ -14,5 +14,9 @@ proc-macro2 = "0.4"
 quote = "0.6"
 syn = "0.15"
 
+[features]
+default = ["std"]
+std = []
+
 [workspace]
 members = ["testcrate"]

README.md

@@ -10,6 +10,8 @@ way to initialise a struct or an enum.
 Implementation uses macros 1.1 custom derive (which works in stable Rust from
 1.15 onwards).
 
+`#[no_std]` is fully supported if you switch off the default feature `"std"`.
+
 ## Examples
 
 Cargo.toml:

src/lib.rs

@@ -254,7 +254,11 @@ enum FieldAttr {
 impl FieldAttr {
     pub fn as_tokens(&self) -> proc_macro2::TokenStream {
         match *self {
-            FieldAttr::Default => my_quote!(::std::default::Default::default()),
+            FieldAttr::Default => if cfg!(feature = "std") {
+                my_quote!(::std::default::Default::default())
+            } else {
+                my_quote!(::core::default::Default::default())
+            },
             FieldAttr::Value(ref s) => my_quote!(#s),
         }
     }
@@ -371,7 +375,11 @@ impl<'a> FieldExt<'a> {
     pub fn as_init(&self) -> proc_macro2::TokenStream {
         let f_name = &self.ident;
         let init = if self.is_phantom_data() {
-            my_quote!(::std::marker::PhantomData)
+            if cfg!(feature = "std") {
+                my_quote!(::std::marker::PhantomData)
+            } else {
+                my_quote!(::core::marker::PhantomData)
+            }
         } else {
             match self.attr {
                 None => my_quote!(#f_name),