I'm trying to see how GTEST_FOUND is set when find_package(GTest REQUIRED) is called, but there's no sign of the variable GTEST_FOUND being set in this file:
https://github.com/Kitware/CMake/blob/master/Modules/FindGTest.cmake
Does anyone know how the variable is set if it's not done in FindGTest.cmake?
The GTEST_FOUND variable is actually set in the FindPackageHandleStandardArgs.cmake file. You can see in FindGTest.cmake, a call to this function is made here:
include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
FIND_PACKAGE_HANDLE_STANDARD_ARGS(GTest DEFAULT_MSG GTEST_LIBRARY GTEST_INCLUDE_DIR GTEST_MAIN_LIBRARY)
The FIND_PACKAGE_HANDLE_STANDARD_ARGS function uses the first argument for the package name (GTest in this case) to set the <PackageName>_FOUND variable.
Here is a quote from the header information for the FIND_PACKAGE_HANDLE_STANDARD_ARGS function:
The <PackageName>_FOUND variable will be set to TRUE if all
the variables <required-var>... are valid and any optional
constraints are satisfied, and FALSE otherwise. A success or
failure message may be displayed based on the results and on
whether the REQUIRED and/or QUIET option was given to
the :command:find_package call.
The code
Using m_objSqlConnection = New SqlCeConnection(m_strConnectionString)
End Using
produces the following error:
Variable 'm_objSqlConnection' hides a variable in an enclosing block
The "m_" prefix suggests that you have a member variable with that name. When you use a Using statement you are declaring a variable that exists only in the scope of that block. If you already have a member variable with that name then why would you want a local variable with the same name? You need to decide whether a local variable or a member variable is more appropriate and stick with the one option. If you're disposing the connection at the end of the Using block then you're apparently not reusing it so I'd think that getting rid of the member variable is the way to go.
If I do:
set(SourceDir ${CMAKE_CURRENT_SOURCE_DIR} PARENT_SCOPE)
message("SourceDir: " ${SourceDir})
The message says that SourceDir is empty. Presumably it is being set in the parent scope only. Is there a way to set the variable in the current scope AND the parent scope? So that I don't have to do:
set(SourceDir ${CMAKE_CURRENT_SOURCE_DIR} PARENT_SCOPE)
set(SourceDir ${CMAKE_CURRENT_SOURCE_DIR})
message("SourceDir: " ${SourceDir})
When you set it for PARENT_SCOPE, it doesn't do it for current scope somehow. But a two step process works. The first line sets it locally, the second line exports it to the parent scope.
set (LIB_VER 6)
set (LIB_VER ${LIB_VER} PARENT_SCOPE)
I think you can not. The documentation says:
Each new directory or function creates a new scope.
If I understand it correctly when your SET gets executed, its scope is already created by copying the parent scope. So no matter what you do to the original (PARENT_SCOPE) your local scope won't change.
You'd better ask the question on CMake's user list to verify that they don't do fallback to parent when a variable is not defined in the local scope. If they do however, this is a bug.
In Elisp I have introduced for a special custom mode a variable like:
(defvar leo-special-var "")
(make-variable-buffer-local 'leo-special-var)
Now I set this variable in files I with the lines (in the file to edit):
# Local Variables:
# leo-special-var: "-d http://www.google.com.au"
# End:
And I want to consider this variable as "safe for all its values. That's why safe-local-variable-values doesn't help. Instead I tried (in the lisp code):
# setting the symbol property of the variable
(put 'leo-special-var 'safe-local-variable 'booleanp)
but without success. Do I do something wrong when setting the symbol property? Or is there another way?
You want to use
(put 'leo-special-var 'safe-local-variable #'stringp)
to say that it is safe as long as it's a string.
If you really want to state that it is safe for all values then use this:
(put 'leo-special-var 'safe-local-variable (lambda (_) t))
The function to test safety here returns non-nil for any value.
(But I'd think that you probably do not want to state that a variable is safe for any value.)
It's in the manual: (elisp) File Local Variables
You can specify safe values for a variable with a
`safe-local-variable' property. The property has to be a function of
one argument; any value is safe if the function returns non-`nil' given
that value. Many commonly-encountered file variables have
`safe-local-variable' properties; these include `fill-column',
`fill-prefix', and `indent-tabs-mode'. For boolean-valued variables
that are safe, use `booleanp' as the property value. Lambda
expressions should be quoted so that `describe-variable' can display
the predicate.
When defining a user option using `defcustom', you can set its
`safe-local-variable' property by adding the arguments `:safe FUNCTION'
to `defcustom' (*note Variable Definitions::).
I'm completely confused by Lua's variable scoping and function argument passing (value or reference).
See the code below:
local a = 9 -- since it's define local, should not have func scope
local t = {4,6} -- since it's define local, should not have func scope
function moda(a)
a = 10 -- creates a global var?
end
function modt(t)
t[1] = 7 -- create a global var?
t[2] = 8
end
moda(a)
modt(t)
print(a) -- print 9 (function does not modify the parent variable)
print(t[1]..t[2]) -- print 78 (some how modt is modifying the parent t var)
As such, this behavior completely confuses me.
Does this mean that table variables
are passed to the function by
reference and not value?
How is the global variable creation
conflicting with the already define
local variable?
Why is modt able to
modify the table yet moda is not able
to modify the a variable?
You guessed right, table variables are passed by reference. Citing Lua 5.1 Reference Manual:
There are eight basic types in Lua: nil, boolean, number, string, function, userdata, thread, and table.
....
Tables, functions, threads, and (full) userdata values are objects: variables do not actually contain these values, only references to them. Assignment, parameter passing, and function returns always manipulate references to such values; these operations do not imply any kind of copy.
So nil, booleans, numbers and strings are passed by value. This exactly explains the behavior you observe.
Lua's function, table, userdata and thread (coroutine) types are passed by reference. The other types are passed by value. Or as some people like to put it; all types are passed by value, but function, table, userdata and thread are reference types.
string is also a kind of reference type, but is immutable, interned and copy-on-write - it behaves like a value type, but with better performance.
Here's what's happening:
local a = 9
local t = {4,6}
function moda(a)
a = 10 -- sets 'a', which is a local introduced in the parameter list
end
function modt(t)
t[1] = 7 -- modifies the table referred to by the local 't' introduced in the parameter list
t[2] = 8
end
Perhaps this will put things into perspective as to why things are the way they are:
local a = 9
local t = {4,6}
function moda()
a = 10 -- modifies the upvalue 'a'
end
function modt()
t[1] = 7 -- modifies the table referred to by the upvalue 't'
t[2] = 8
end
-- 'moda' and 'modt' are closures already containing 'a' and 't',
-- so we don't have to pass any parameters to modify those variables
moda()
modt()
print(a) -- now print 10
print(t[1]..t[2]) -- still print 78
jA_cOp is correct when he says "all types are passed by value, but function, table, userdata and thread are reference types."
The difference between this and "tables are passed by reference" is important.
In this case it makes no difference,
function modt_1(x)
x.foo = "bar"
end
Result: both "pass table by reference" and "pass table by value, but table is a reference type" will do the same: x now has its foo field set to "bar".
But for this function it makes a world of difference
function modt_2(x)
x = {}
end
In this case pass by reference will result in the argument getting changed to the empty table. However in the "pass by value, but its a reference type", a new table will locally be bound to x, and the argument will remain unchanged. If you try this in lua you will find that it is the second (values are references) that occurs.
I won't repeat what has already been said on Bas Bossink and jA_cOp's answers about reference types, but:
-- since it's define local, should not have func scope
This is incorrect. Variables in Lua are lexically scoped, meaning they are defined in a block of code and all its nested blocks.
What local does is create a new variable that is limited to the block where the statement is, a block being either the body of a function, a "level of indentation" or a file.
This means whenever you make a reference to a variable, Lua will "scan upwards" until it finds a block of code in which that variable is declared local, defaulting to global scope if there is no such declaration.
In this case, a and t are being declared local but the declaration is in global scope, so a and t are global; or at most, they are local to the current file.
They are then not being redeclared local inside the functions, but they are declared as parameters, which has the same effect. Had they not been function parameters, any reference inside the function bodies would still refer to the variables outside.
There's a Scope Tutorial on lua-users.org with some examples that may help you more than my attempt at an explanation. Programming in Lua's section on the subject is also a good read.
Does this mean that table variables are passed to the function by reference and not value?
Yes.
How is the global variable creation conflicting with the already define local variable?
It isn't. It might appear that way because you have a global variable called t and pass it to a function with an argument called t, but the two ts are different. If you rename the argument to something else, e,g, q the output will be exactly the same. modt(t) is able to modify the global variable t only because you are passing it by reference. If you call modt({}), for example, the global t will be unaffected.
Why is modt able to modify the table yet moda is not able to modify the a variable?
Because arguments are local. Naming your argument a is similar to declaring a local variable with local a except obviously the argument receives the passed-in value and a regular local variable does not. If your argument was called z (or was not present at all) then moda would indeed modify the global a.