This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of NAD status.
Section: 3.2 [dec.tr::trdec.types.types] Status: NAD Submitter: Martin Sebor Opened: 2006-06-15 Last modified: 2016-01-31
Priority: Not Prioritized
View all other issues in [dec.tr::trdec.types.types].
View all issues with NAD status.
Discussion:
In c++std-lib-17205, Martin writes:
...was it a deliberate design choice to make narrowing assignments ill-formed while permitting narrowing compound assignments? For instance:
decimal32 d32;
decimal64 d64;
d32 = 64; // error
d32 += 64; // okay
In c++std-lib-17229, Robert responds:
It is a vestige of an old idea that I forgot to remove from the paper. Narrowing assignments should be permitted. The bug is that the converting constructors that cause narrowing should not be explicit. Thanks for pointing this out.
[ 2009-07 Frankfurt ]
The current state of the Decimal TR is the result of a deliberate design decision that has been examined many times.
Move to NAD.
Proposed resolution:
1. In "3.2.2 Class decimal32" synopsis, remove the explicit specifier from the narrowing conversions:
// 3.2.2.2 conversion from floating-point type:
explicit decimal32(decimal64 d64);
explicit decimal32(decimal128 d128);
2. Do the same thing in "3.2.2.2. Conversion from floating-point type."
3. In "3.2.3 Class decimal64" synopsis, remove the explicit specifier from the narrowing conversion:
// 3.2.3.2 conversion from floating-point type:
explicit decimal64(decimal128 d128);
4. Do the same thing in "3.2.3.2. Conversion from floating-point type."
[ Redmond: We prefer explicit conversions for narrowing and implicit for widening. ]