• Steven Schveighoffer (12/12) Jan 13 2020 I have a range (array), I want to find an element and get it from that
• H. S. Teoh (13/29) Jan 13 2020 [...]
• Steven Schveighoffer (4/15) Jan 13 2020 I certainly can (and did). I was wondering if there was something in
• H. S. Teoh (6/21) Jan 13 2020 [...]
• lithium iodate (15/30) Jan 13 2020 `adjoin` can be used to run an inline lambda:

Steven Schveighoffer <schveiguy gmail.com> writes:

I have a range (array), I want to find an element and get it from that 
array.

The code I'm writing looks like this:

auto answer = arr.find!((item,x) => item.id == x)(id);
enforce(!answer.empty, "id not in the range");
auto realAnswer = answer.front;

I can't do find(id).front, because that relies on asserts, which throw 
errors and kill the program, and are not always compiled in. I need an 
exception thrown so I can recover and report the error to the user.

But I hate to write 3 lines of code to do this every time.

I'm not seeing an easy solution in Phobos, am I missing it?

-Steve

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Mon, Jan 13, 2020 at 12:39:30PM -0500, Steven Schveighoffer via
Digitalmars-d-learn wrote:
 I have a range (array), I want to find an element and get it from that
 array.
 
 The code I'm writing looks like this:
 
 auto answer = arr.find!((item,x) => item.id == x)(id);
 enforce(!answer.empty, "id not in the range");
 auto realAnswer = answer.front;
 
 I can't do find(id).front, because that relies on asserts, which throw
 errors and kill the program, and are not always compiled in. I need an
 exception thrown so I can recover and report the error to the user.
 
 But I hate to write 3 lines of code to do this every time.
 
 I'm not seeing an easy solution in Phobos, am I missing it?

[...]

Why not write your own convenience wrapper?

	auto firstElement(R)(R r)
		if (isInputRange!R)
	{
		if (r.empty) throw new Exception(...);
		return r.front;
	}

	auto e = myData.find!(e => blah(e)).firstElement;


T

-- 
I think Debian's doing something wrong, `apt-get install pesticide', doesn't
seem to remove the bugs on my system! -- Mike Dresser

Steven Schveighoffer <schveiguy gmail.com> writes:

On 1/13/20 12:47 PM, H. S. Teoh wrote:
 
 Why not write your own convenience wrapper?
 
 	auto firstElement(R)(R r)
 		if (isInputRange!R)
 	{
 		if (r.empty) throw new Exception(...);
 		return r.front;
 	}
 
 	auto e = myData.find!(e => blah(e)).firstElement;

I certainly can (and did). I was wondering if there was something in 
Phobos to do it.

-Steve

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Mon, Jan 13, 2020 at 12:58:57PM -0500, Steven Schveighoffer via
Digitalmars-d-learn wrote:
 On 1/13/20 12:47 PM, H. S. Teoh wrote:
 
 Why not write your own convenience wrapper?
 
 	auto firstElement(R)(R r)
 		if (isInputRange!R)
 	{
 		if (r.empty) throw new Exception(...);
 		return r.front;
 	}
 
 	auto e = myData.find!(e => blah(e)).firstElement;

 
 I certainly can (and did). I was wondering if there was something in
 Phobos to do it.

[...]

Maybe add a new function to Phobos? :-D


T

-- 
It always amuses me that Windows has a Safe Mode during bootup. Does that mean
that Windows is normally unsafe?

lithium iodate <whatdoiknow doesntexist.net> writes:

On Monday, 13 January 2020 at 17:58:57 UTC, Steven Schveighoffer 
wrote:
 On 1/13/20 12:47 PM, H. S. Teoh wrote:
 
 Why not write your own convenience wrapper?
 
 	auto firstElement(R)(R r)
 		if (isInputRange!R)
 	{
 		if (r.empty) throw new Exception(...);
 		return r.front;
 	}
 
 	auto e = myData.find!(e => blah(e)).firstElement;

 I certainly can (and did). I was wondering if there was 
 something in Phobos to do it.

 -Steve

`adjoin` can be used to run an inline lambda:
auto answer = arr.find!((item,x) => item.id == 
x)(id).adjoin!((n){enforce(!n.empty); return n.front;});

Using a simple alias you can have a flexible and nice to read 
solution:
alias ensure(alias pred) = (n, const(char)[] msg = "`ensure` 
failed"){enforce(pred(n), msg); return n;}; // module scope for 
UFCS!

auto answer = arr.find!((item,x) => item.id == x)(id).ensure!(n 
=> !n.empty).front;
or with custom message:
auto answer = arr.find!((item,x) => item.id == x)(id).ensure!(n 
=> !n.empty)("element with id not found").front;