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digitalmars.D.learn - Help, what is the code mean?

reply lilijreey <lilijreey 126.com> writes:
Hi:
    In dlang core.thread.osthread has below code, the 654 line 
code i can understand why write () first, and {m_fn = fn;}()  do 
what?
```
    this( void function() fn, size_t sz = 0 )  safe pure nothrow 
 nogc
    647     in
    648     {
    649         assert( fn );
    650     }
    651     do
    652     {
    653         this(sz);
    654         ()  trusted { m_fn   = fn; }(); //What is the code 
mean?
    655         m_call = Call.FN;
    656         m_curr = &m_main;
    657     }
```
Apr 27 2020
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Monday, 27 April 2020 at 13:29:08 UTC, lilijreey wrote:

 Hi:
    In dlang core.thread.osthread has below code, the 654 line 
 code i can understand why write () first, and {m_fn = fn;}()  
 do what?


The stdlib uses that pattern from time to time to indicate an 
unsafe block in an otherwise safe function.

Specifically it is a little trusted inline function being 
immediately called.

It is something that should be avoided whenever you can.
Apr 27 2020
next sibling parent reply lilijreey <lilijreey 126.com> writes:
 The stdlib uses that pattern from time to time to indicate an 
 unsafe block in an otherwise safe function.

 Specifically it is a little trusted inline function being 
 immediately called.

 It is something that should be avoided whenever you can.


Thanks your help. where is unsafe in above code?
Apr 27 2020
parent Adam D. Ruppe <destructionator gmail.com> writes:
On Monday, 27 April 2020 at 15:24:09 UTC, lilijreey wrote:

 Thanks your help. where is unsafe in above code?


It depends on the context but I assume it is because it is 
storing a reference to the function across thread boundaries, 
something normally banned, but since it is (I believe) a private 
member it is promising the compiler "trust me, I'm doing this 
implementation detail right". Hence the keyword " trusted".

This is not the way that keyword was originally designed to be 
used, hence the janky syntax, but the stdlib authors use the 
pattern in a few places anyway.
Apr 27 2020
prev sibling next sibling parent reply data pulverizer <data.pulverizer gmail.com> writes:
On Monday, 27 April 2020 at 13:36:25 UTC, Adam D. Ruppe wrote:

 On Monday, 27 April 2020 at 13:29:08 UTC, lilijreey wrote:

 Hi:
    In dlang core.thread.osthread has below code, the 654 line 
 code i can understand why write () first, and {m_fn = fn;}()  
 do what?


 The stdlib uses that pattern from time to time to indicate an 
 unsafe block in an otherwise safe function.

 Specifically it is a little trusted inline function being 
 immediately called.

 It is something that should be avoided whenever you can.


I'm probably not the first person to say this but. Isn't  trusted 
an odd label to give unsafe functions and open to abuse by 
unscrupulous programmers? It almost says "nothing to see, this 
here piece of code is a-ok". Shouldn't it be explicitly labelled 
as  unsafe?
Apr 27 2020
parent reply drug <drug2004 bk.ru> writes:
27.04.2020 18:28, data pulverizer пишет:

 I'm probably not the first person to say this but. Isn't  trusted an odd 
 label to give unsafe functions and open to abuse by unscrupulous 
 programmers? It almost says "nothing to see, this here piece of code is 
 a-ok". Shouldn't it be explicitly labelled as  unsafe?


It says "this piece of code is verified by its author manually so you 
(the compiler) can trust it is  safe"
Apr 27 2020
parent Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Monday, April 27, 2020 9:52:32 AM MDT drug via Digitalmars-d-learn wrote:

 27.04.2020 18:28, data pulverizer пишет:

 I'm probably not the first person to say this but. Isn't  trusted an odd
 label to give unsafe functions and open to abuse by unscrupulous
 programmers? It almost says "nothing to see, this here piece of code is
 a-ok". Shouldn't it be explicitly labelled as  unsafe?


 It says "this piece of code is verified by its author manually so you
 (the compiler) can trust it is  safe"


Exactly.  trusted isn't about marking something as not being memory safe.
The compiler already treats anything as not being memory safe if it can't
verify that it's memory safe. It's about the programmer telling the compiler
that they've verified that it's memory safe even though the compiler
couldn't. The code that neither the programmer nor the compiler has verified
to be memory safe is  system. So, if we had the attribute  unsafe, it would
have been instead of  system, not  trusted.

And ultimately,  trusted is not about telling anyone that there's "nothing
to see." If anything, it's the opposite.  trusted code is the primary place
that has to be examined when you have a memory bug in your code (or think
that you have one). Barring bugs in the compiler, it should not be possible
for  safe code to do anything that's memory unsafe, so when looking for
memory safety bugs, it's the  trusted code that has to be examined to make
sure that it actually is memory safe and that the programmer didn't use
 trusted correctly.

- Jonathan M Davis
Apr 28 2020
prev sibling parent reply Net <netorib94 gmail.com> writes:
On Monday, 27 April 2020 at 13:36:25 UTC, Adam D. Ruppe wrote:

 On Monday, 27 April 2020 at 13:29:08 UTC, lilijreey wrote:

 Hi:
    In dlang core.thread.osthread has below code, the 654 line 
 code i can understand why write () first, and {m_fn = fn;}()  
 do what?


 The stdlib uses that pattern from time to time to indicate an 
 unsafe block in an otherwise safe function.

 Specifically it is a little trusted inline function being 
 immediately called.

 It is something that should be avoided whenever you can.


() { ... } ();

Is there a name of this kind of function in D? unnamed? anonymous?
Apr 28 2020
next sibling parent ag0aep6g <anonymous example.com> writes:
On Tuesday, 28 April 2020 at 20:48:57 UTC, Net wrote:

 () { ... } ();

 Is there a name of this kind of function in D? unnamed? 
 anonymous?


The spec uses "anonymous". Syntactically, `() { ... }` is a 
function literal.

There is a section called "Anonymous Functions and Anonymous 
Delegates" [1], but it's just a link to "Function Literals":

https://dlang.org/spec/expression.html#function_literals

To be clear, the second set of parentheses in `() { ... } ()` 
just calls the anonymous function. You could equivalently write 
it like this:

     alias f = () { ... };
     f();


[1] https://dlang.org/spec/function.html#anonymous
Apr 28 2020
prev sibling parent =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 4/28/20 1:48 PM, Net wrote:

 () { ... } ();

 Is there a name of this kind of function in D? unnamed? anonymous?


Lambda or anonymous function.[1]

Note that the last () is not part of the definition but the execution of 
the function.

This idiom is used for initializing e.g. a const variable with 
non-trivial code as well (in C++ as well):

const a = {
     // ... some complex logic ...
     return result;
   }();

Ali

[1] I have a page that shows different syntaxes for lambda functions:

   http://ddili.org/ders/d.en/lambda.html#ix_lambda.=%3E
Apr 28 2020