• Jack (11/14) Oct 14 2020 ?
• Paul Backus (10/24) Oct 14 2020 The difference is that the first version gives you a `void[]`,
• Jack (4/15) Oct 15 2020 My bad, the first one doesn't perform bounds-checking.So it just
• =?UTF-8?Q?Ali_=c3=87ehreli?= (6/8) Oct 14 2020 https://wiki.dlang.org/Memory_Management#Explicit_Class_Instance_Allocat...
• Jack (2/10) Oct 15 2020 make sense, thanks

Jack <jckj33 gmail.com> writes:

What's the difference between:

import core.stdc.stdlib : malloc;
auto x = malloc(s)[0..s];

and
auto x = cast(T)malloc(s);

?

I have been using the last but I saw in some code examples, like 
this[1] the first being used. What's the difference? in the first 
one bounds checking is performed, giving an error right away, 
right? whereas the cast would just turn the null into the class 
reference and manual check need to be done later. Is that the 
reason?

[1]: 
https://wiki.dlang.org/Memory_Management#Explicit_Class_Instance_Allocation

Paul Backus <snarwin gmail.com> writes:

On Wednesday, 14 October 2020 at 20:15:39 UTC, Jack wrote:
 What's the difference between:

import core.stdc.stdlib : malloc;
auto x = malloc(s)[0..s];

 and
auto x = cast(T)malloc(s);

 ?

 I have been using the last but I saw in some code examples, 
 like this[1] the first being used. What's the difference? in 
 the first one bounds checking is performed, giving an error 
 right away, right? whereas the cast would just turn the null 
 into the class reference and manual check need to be done 
 later. Is that the reason?

 [1]: 
 https://wiki.dlang.org/Memory_Management#Explicit_Class_Instance_Allocation

The difference is that the first version gives you a `void[]`, 
and the second version gives you a `T`. Neither version does any 
bounds checking.

Generally, you'd use the first version if you don't yet know what 
kind of object is going to be stored in the allocated memory (for 
example, if you're writing an allocator[1]), and the second 
version if you do know the type.

[1] 
https://dlang.org/phobos/std_experimental_allocator_building_blocks.html

Jack <jckj33 gmail.com> writes:

On Wednesday, 14 October 2020 at 21:12:13 UTC, Paul Backus wrote:
 On Wednesday, 14 October 2020 at 20:15:39 UTC, Jack wrote:
 [...]

 The difference is that the first version gives you a `void[]`, 
 and the second version gives you a `T`. Neither version does 
 any bounds checking.

 Generally, you'd use the first version if you don't yet know 
 what kind of object is going to be stored in the allocated 
 memory (for example, if you're writing an allocator[1]), and 
 the second version if you do know the type.

 [1] 
 https://dlang.org/phobos/std_experimental_allocator_building_blocks.html

My bad, the first one doesn't perform bounds-checking.So it just 
depends on context, where you are going to use the result from 
malloc()

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 10/14/20 1:15 PM, Jack wrote:

 auto x = malloc(s)[0..s];


 

https://wiki.dlang.org/Memory_Management#Explicit_Class_Instance_Allocation

Note that 'x' is passed to emplace() at that link and emplace() requires 
a slice. That's why the a slice is made from the pointer returned by 
malloc().

Ali

Jack <jckj33 gmail.com> writes:

On Thursday, 15 October 2020 at 01:22:54 UTC, Ali Çehreli wrote:
 On 10/14/20 1:15 PM, Jack wrote:

 auto x = malloc(s)[0..s];


 

 https://wiki.dlang.org/Memory_Management#Explicit_Class_Instance_Allocation

 Note that 'x' is passed to emplace() at that link and emplace() 
 requires a slice. That's why the a slice is made from the 
 pointer returned by malloc().

 Ali

make sense, thanks