If I have a function with optional parameter, is there an easy way to find all the locations in my code that call that function and pass a value to that parameter?
The function has many non-default parameters, so scanning the usual Find Usages results of places that call the function is problematic, as it trims the lines and I can't see if the optional parameter is used.
With your cursor on the parameter, choose ReSharper | Inspect | Value Origin, or from the keyboard, Inspect This with Ctrl+Shift+Alt+A, then Value Origin.
You will get an Inspection Results window with all the places that explicitly assign that parameter a value.
I think the best way is changing Signature of the method. In other word you can change type of the parameter to another type (that is not used by parameters for safety) and see Errors list after rebuild.
By this way you can find all (not only explicitly) usages of the parameter.
Related
Is there a way to do the following in a html/template?
{{template "mytemplate" struct{Foo1, Foo2 string}{"Bar1", "Bar2"}}}
Actually in the template, like above. Not via a function registered in FuncMap which returns the struct.
I tried it, but Parse panics, see Playground. Maybe just the syntax is wrong?
As noted by others, it's not possible. Templates are parsed at runtime, without the help of the Go compiler. So allowing arbitrary Go syntax would not be feasible (although note that it wouldn't be impossible, as the standard lib contains all the tools to parse Go source text, see packages "prefixed" with go/ in the standard lib). By design philosophy, complex logic should be outside of templates.
Back to your example:
struct{Foo1, Foo2 string}{"Bar1", "Bar2"}
This is a struct composite literal and it is not supported in templates, neither when invoking another template nor at other places.
Invoking another template with a custom "argument" has the following syntax (quoting from text/template: Actions):
{{template "name" pipeline}}
The template with the specified name is executed with dot set
to the value of the pipeline.
TL;DR; A pipeline may be a constant, an expression denoting a field or method of some value (where the method will be called and its return value will be used), it may be a call to some "template-builtin" function or a custom registered function, or a value in a map.
Where Pipeline is:
A pipeline is a possibly chained sequence of "commands". A command is a simple value (argument) or a function or method call, possibly with multiple arguments:
Argument
The result is the value of evaluating the argument.
.Method [Argument...]
The method can be alone or the last element of a chain but,
unlike methods in the middle of a chain, it can take arguments.
The result is the value of calling the method with the
arguments:
dot.Method(Argument1, etc.)
functionName [Argument...]
The result is the value of calling the function associated
with the name:
function(Argument1, etc.)
Functions and function names are described below.
And an Argument is:
An argument is a simple value, denoted by one of the following.
- A boolean, string, character, integer, floating-point, imaginary
or complex constant in Go syntax. These behave like Go's untyped
constants. Note that, as in Go, whether a large integer constant
overflows when assigned or passed to a function can depend on whether
the host machine's ints are 32 or 64 bits.
- The keyword nil, representing an untyped Go nil.
- The character '.' (period):
.
The result is the value of dot.
- A variable name, which is a (possibly empty) alphanumeric string
preceded by a dollar sign, such as
$piOver2
or
$
The result is the value of the variable.
Variables are described below.
- The name of a field of the data, which must be a struct, preceded
by a period, such as
.Field
The result is the value of the field. Field invocations may be
chained:
.Field1.Field2
Fields can also be evaluated on variables, including chaining:
$x.Field1.Field2
- The name of a key of the data, which must be a map, preceded
by a period, such as
.Key
The result is the map element value indexed by the key.
Key invocations may be chained and combined with fields to any
depth:
.Field1.Key1.Field2.Key2
Although the key must be an alphanumeric identifier, unlike with
field names they do not need to start with an upper case letter.
Keys can also be evaluated on variables, including chaining:
$x.key1.key2
- The name of a niladic method of the data, preceded by a period,
such as
.Method
The result is the value of invoking the method with dot as the
receiver, dot.Method(). Such a method must have one return value (of
any type) or two return values, the second of which is an error.
If it has two and the returned error is non-nil, execution terminates
and an error is returned to the caller as the value of Execute.
Method invocations may be chained and combined with fields and keys
to any depth:
.Field1.Key1.Method1.Field2.Key2.Method2
Methods can also be evaluated on variables, including chaining:
$x.Method1.Field
- The name of a niladic function, such as
fun
The result is the value of invoking the function, fun(). The return
types and values behave as in methods. Functions and function
names are described below.
- A parenthesized instance of one the above, for grouping. The result
may be accessed by a field or map key invocation.
print (.F1 arg1) (.F2 arg2)
(.StructValuedMethod "arg").Field
The proper solution would be to register a custom function that constructs the value you want to pass to the template invocation, as you can see in this related / possible duplicate: Golang pass multiple values from template to template?
Another, half solution could be to use the builtin print or printf functions to concatenate the values you want to pass, but that would require to split in the other template.
As mentioned by #icza, this is not possible.
However, you might want to provide a generic dict function to templates to allow to build a map[string]interface{} from a list of arguments. This is explained in this other answer: https://stackoverflow.com/a/18276968/328115
I was working on a simple task yesterday, just needed to sum the values in a handful of dropdown menus to display in a textbox via Javascript. Unexpectedly, it was just building a string so instead of giving me the value 4 it gave me "1111". I understand what was happening; but I don't understand how.
With a loosely typed language like Javascript or PHP, how does the computer "know" what type to treat something as? If I just type everything as a var, how does it differentiate a string from an int from an object?
What the + operator will do in Javascript is determined at runtime, when both actual arguments (and their types) are known.
If the runtime sees that one of the arguments is a string, it will do string concatenation. Otherwise it will do numeric addition (if necessary coercing the arguments into numbers).
This logic is coded into the implementation of the + operator (or any other function like it). If you looked at it, you would see if typeof(a) === 'string' statements (or something very similar) in there.
If I just type everything as a var
Well, you don't type it at all. The variable has no type, but any actual value that ends up in that variable has a type, and code can inspect that.
Is it possible in Visual Foxpro to have 2 variables that point to the same address in memory. Such that if the value of one of the variables is changed then the other is also changed. I understand that when passing arguments to functions they can be passed by value or reference but I want to know if this is possible in straight code. I think in other languages such as C this is called a pointer but I don't believe VFP has pointers. So if one writes the following code it will output the number 4.
a=4
b=a
a=6
? b && answer 4
But could one write code such as the following where the answer could be 6?
a=4
b=*a && note the inclusion of the asterisk (pointer?) here which won't compile in VFP
a=6
? b
No. There are no pointers or references in Foxpro; as you note, the closest thing to it is passing parameters by reference to functions. You might be able to try to kludge something together (as Jerry mentions) with objects using Access/Assign methods, but even then, all that gets passed to the Assign method is the value being assigned - nothing about whether it was originally another variable, a literal value, an object's property, etc.
You could simulate it by using an array or a table. The variables would contain only the array index or record number (or other index) as a reference, and you'd have to get the actual value from the array or table.
Take a look at the Visual Foxpro Access and Assign Methods. These methods can be used to execute code when querying a property or trying to change the value of a property. Below is a link that shows an example:
Access and Assign Example
You could do something like this:
a=4
b='a'
a=6
?&b
When creating a tracepoint in Visual Studio (right-click the breakpoint and choose "When Hit..."), the dialog has this text, emphasis mine:
You can include the value of a variable or other expression in the message by placing it in curly braces...
What expressions are allowed?
Microsoft's documentation is rather sparse on the exact details of what is and is not allowed. Most of the below was found by trial and error in the Immediate window. Note that this list is for C++, as that's what I code in. I believe in C#, some of the prohibited items below are actually allowed.
Most basic expressions can be evaluated, including casting, setting variables, and calling functions.
General Restrictions
Only C-style casts supported; no static_cast, dynamic_cast, reinterpret_cast, const_cast
Can't declare new variables or create objects
Can't use overloaded operators
Ternary operator doesn't work
Can't use the comma operator because Visual Studio uses it to format the result of the expression; use multiple sets of braces for multiple expressions
Function Calls
Prohibited calls:
Lambdas (can't define or call them)
Functions in an anonymous namespace
Functions that take objects by value (because you can't create objects)
Permitted calls:
Member functions, both regular and virtual
Functions taking references or pointers, to either fundamental or class types
Passing in-scope variables
Using "&" to pass pointers to in-scope variables
Passing the literals "true", "false", numbers
Passing string literals, as long you don't run afoul of the "can't create objects" rule
Calling multiple functions with one tracepoint by using multiple sets of braces
Variable Assignment
Prohibited:
Objects
String literals
Permitted:
Variables with fundamental types, value either from literals or other variables
Memory addresses, after casting: { *(bool*)(0x1234) = true }
Registers: { #eip = 0x1234 }
Use Cases
Calling functions from tracepoints can be quite powerful. You can get around most of the restrictions listed above with a carefully set up function and the right call. Here are some more specific ideas.
Force an if
Pretty straightforward: set up a tracepoint to set a variable and force an if-condition to true or false, depending on what you need to test. All without adding code or leaving the debug session.
Breakpoint "toggling"
I've seen the question a few times, "I need to break in a spot that gets hit a lot. I'd like to simply enable that breakpoint from another breakpoint, so the one I care about only gets breaks from a certain code path. How can I do that?" With our knowledge above, it's easy, although you do need a helper variable.
Create a global boolean, set to false.
Create a breakpoint at your final destination, with a condition to break only when the global flag is true.
Set tracepoints in the critical spots that assign the global flag to true.
The nice thing is that you can move the tracepoints around without leaving the debugging session. Use the Immediate window or the Watch window to reset your global flag, if you need to make another run at it. When you're done, all you need to clean up is that global boolean. No other code to remove.
Automatically skip code
The EIP register (at least on x86) is the instruction pointer. If you assign to it, you can change your program flow.
Find the address of the line you want to skip to by breaking on it once and looking at the value of EIP, either in the Registers window or the Watch window with "#eip,x". (Note that the value in the Registers window is hex, but without the leading "0x".)
Add a tracepoint on the line you want to skip from, with an expression like {#eip = address}, using the address from step 1.
EIP assignment will happen before anything on the line is executed.
Although this can be handy, be careful because skipping code like this can cause weird behavior.
As Kurt Hutchinson says, string assignment is not allowed in a tracepoint. You can get around this by creating a method that assigns the string variable, and call that.
public static class Helper
{
public static void AssignTo(this string value, out string variable)
{
variable = value;
}
}
Then in your tracepoint message:
{"new string value".AssignTo(out stringVariable)}
At work we often use functions returning a BOOLEAN where the BOOLEAN represents a logical statement and not whether the operation of the function was successfully or not
e.g. BOOLEAN HaseThisValueBeCountedAlready (Value)
When validating the input in this function what would be the best way proceed if invalid input was detected. Some people think to just return FALSE but in my opinion that would just hide the fact that something is wrong and the Caller might proceed doing something with the value not knowing that the answer doesn't make sense.
The function might be globally accessible so it feels a bit weird assuming the caller will validate the input.
Any ideas?
In general, for invalid input that doesn't enable the functions to provide the service/answer, you need to raise an exception.
This way, the guy asking the "question" to the function knows he's not "formulating" it the right way.
if its a value that need to be read periodically , you can assign the output to a global variable ,if it valid or dont update global variable if the input is invalid , so the global variable stays with the previous valid value.
this way , each function need this value , use the global variable with 100% that is valid value.