diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md
index 6d1eb7e..d5895a6 100644
--- a/CppCoreGuidelines.md
+++ b/CppCoreGuidelines.md
@@ -10647,15 +10647,20 @@ For initializers of moderate complexity, including for `const` variables, consid
* Flag declarations with default initialization that are assigned to before they are first read.
* Flag any complicated computation after an uninitialized variable and before its use.
-### ES.23: Prefer the `{}` initializer syntax
+### ES.23: Prefer the `{}`-initializer syntax
##### Reason
-The rules for `{}` initialization are simpler, more general, less ambiguous, and safer than for other forms of initialization.
+Prefer `{}`. The rules for `{}` initialization are simpler, more general, less ambiguous, and safer than for other forms of initialization.
+
+Use `=` only when you are sure that there can be no narrowing conversions. For built-in arithmetic types, use `=` only with `auto`.
+
+Avoid `()` initialization, which allows parsing ambiguities.
##### Example
int x {f(99)};
+ int y = x;
vector v = {1, 2, 3, 4, 5, 6};
##### Exception
@@ -10663,11 +10668,14 @@ The rules for `{}` initialization are simpler, more general, less ambiguous, and
For containers, there is a tradition for using `{...}` for a list of elements and `(...)` for sizes:
vector v1(10); // vector of 10 elements with the default value 0
- vector v2 {10}; // vector of 1 element with the value 10
+ vector v2{10}; // vector of 1 element with the value 10
+
+ vector v3(1, 2); // vector of 1 element with the value 2
+ vector v4{1, 2}; // vector of 2 element with the values 1 and 2
##### Note
-`{}`-initializers do not allow narrowing conversions (and that is usually a good thing).
+`{}`-initializers do not allow narrowing conversions (and that is usually a good thing) and allow explicit constructors (which is fine, we're intentionally initializing a new variable).
##### Example
@@ -10677,7 +10685,7 @@ For containers, there is a tradition for using `{...}` for a list of elements an
##### Note
-`{}` initialization can be used for all initialization; other forms of initialization can't:
+`{}` initialization can be used for nearly all initialization; other forms of initialization can't:
auto p = new vector {1, 2, 3, 4, 5}; // initialized vector
D::D(int a, int b) :m{a, b} { // member initializer (e.g., m might be a pair)
@@ -10698,7 +10706,7 @@ Initialization of a variable declared using `auto` with a single value, e.g., `{
The C++17 rules are somewhat less surprising:
auto x1 {7}; // x1 is an int with the value 7
- auto x2 = {7}; // x2 is an initializer_list with an element 7
+ auto x2 = {7}; // x2 is an initializer_list with an element 7
auto x11 {7, 8}; // error: two initializers
auto x22 = {7, 8}; // x22 is an initializer_list with elements 7 and 8
@@ -10720,10 +10728,6 @@ Like the distinction between copy-initialization and direct-initialization itsel
Use plain `{}`-initialization unless you specifically want to disable explicit constructors.
-##### Note
-
-Old habits die hard, so this rule is hard to apply consistently, especially as there are so many cases where `=` is innocent.
-
##### Example
template
@@ -10741,10 +10745,8 @@ Old habits die hard, so this rule is hard to apply consistently, especially as t
##### Enforcement
-Tricky.
-
-* Don't flag uses of `=` for simple initializers.
-* Look for `=` after `auto` has been seen.
+* Flag uses of `=` to initialize arithmetic types where narrowing occurs.
+* Flag uses of `()` initialization syntax that are actually declarations. (Many compilers should warn on this already.)
### ES.24: Use a `unique_ptr` to hold pointers