From 9029b18fc06533b6ee100c35ba00f9e676f66417 Mon Sep 17 00:00:00 2001
From: Y <theYinYeti@yalis.fr>
Date: Sun, 17 Nov 2019 16:50:48 +0100
Subject: [PATCH] =?UTF-8?q?Box::new=20+=20&[=E2=80=A6]=20notation?=
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---
 README.md | 49 ++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 13 deletions(-)

diff --git a/README.md b/README.md
index 1bb63ba..8f9cd29 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,20 @@
 ## setup
 
+In module `common`, I have:
+
+```rust
+pub enum Value {
+  Bool(bool),
+  Str(String),
+  Int(isize),
+  Date(DateTime<chrono::Utc>)
+}
+
+pub type Record<'a> = HashMap<&'a str, Value>;
+```
+
+(in a future version, `Value` will probably become recursive, with a variant `Vec<Value>` for example)
+
 In module `modules`, I have:
 
 ```rust
@@ -34,35 +49,43 @@ struct Available {
   cons: Box<fn(ModuleArgs) -> dyn Module>
 }
 
-const available: [Available] = [
-  Available { name: "equals", cons: Box.new(filters::Equals::from_args) }
+const available: &[Available] = &[
+  Available { name: String::from("equals"), cons: Box::new(move |a| filters::Equals::from_args(a)) }
 ];
 ```
 
 with `available` being an array of available modules, each having a name and a constructor.
 
+However, I rather fail to see the reason for:
+
+* `Box`: In my case, it will be set forever, and be unmutable; and fn is a pointer anyway, so fixed-size…
+* `&[…]` notation: In this case, `available` is a constant, and I suppose its size is known at compile-time, so there shouldn’t be the need for a reference.
+
 ## problem
 
-The above code gives me these errors (which I suspect are hiding the next error about `"equals"` probably being `&str` instead of `String`…):
+The above code gives me these errors:
 
 * first:
 
   ```
-  error[E0423]: expected value, found struct `Box`
-    --> src/modules.rs:10:37
-     |
-  10 |   Available { name: "equals", cons: Box.new(filters::Equals::from_args) }
-     |                                     ^^^ constructor is not visible here due to private fields
+  error[E0277]: the size for values of type `dyn modules::Module` cannot be known at compilation time
+    --> src/modules.rs:10:69
+    |
+  10 |   Available { name: String::from("equals"), cons: Box::new(move |a| filters::Equals::from_args(a)) }
+    |                                                                     ^ doesn't have a size known at compile-time
+    |
+    = help: the trait `std::marker::Sized` is not implemented for `dyn modules::Module`
   ```
 
 * second:
 
   ```
-  error[E0277]: the size for values of type `[modules::Available]` cannot be known at compilation time
-   --> src/modules.rs:9:18
+  error[E0308]: mismatched types
+    --> src/modules.rs:10:69
     |
-  9 | const available: [Available] = [
-    |                  ^^^^^^^^^^^ doesn't have a size known at compile-time
+  10 |   Available { name: String::from("equals"), cons: Box::new(move |a| filters::Equals::from_args(a)) }
+    |                                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait modules::Module, found struct `filters::Equals`
     |
-    = help: the trait `std::marker::Sized` is not implemented for `[modules::Available]`
+    = note: expected type `dyn modules::Module`
+                found type `filters::Equals`
   ```