#variant issues w/ unique_ptr

17 messages · Page 1 of 1 (latest)

rapid plinthBOT
#

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smoky vector
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i get these errors when i try to do the following:

# 
void Generator::gen_stmt(Stmt stmt)
{
    struct StmtVisitor {
        Generator& gen;

        void operator()(VarStmt var_stmt)
        {
        }
    };

    StmtVisitor stmt_visitor{*this};
    std::visit(stmt_visitor, stmt.m_stmt);
}
#

this is the entire ast

struct Expr;

struct VarStmt {
    std::string m_name{};
    std::unique_ptr<Expr> m_expr{};
};

struct Stmt {
    std::variant<VarStmt> m_stmt{};
};

struct IntExpr {
    int m_value{};
};

struct FloatExpr {
    float m_value{};
};

struct StrExpr {
    std::string m_value{};
};

struct AtomExpr {
    std::variant<IntExpr, FloatExpr, StrExpr> m_atom{};
};

struct BinOpExpr {
    std::unique_ptr<Expr> m_lhs{};
    std::unique_ptr<Expr> m_rhs{};
    Token_Type m_op{};
};

struct Expr {
    std::variant<AtomExpr, BinOpExpr> m_expr{};
};

struct Program {
    std::vector<Stmt> m_body{};
};
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okay, i needed to take VarStmt& instead of VarStmt as an argument

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but I don't understand why

proper crown
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You can't copy a unique_ptr

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You can move it with std::move or pass by reference

smoky vector
proper crown
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Some?

smoky vector
#

the function has to accept a reference to a Stmt

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so that Stmt is not copied

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as it contains a variant that contains a uniqueptr

proper crown
#

Yep exactly

jaunty thistle
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U have to implement
void operator()( VarStmt &var_stmt)
{

}
Instead of
void operator()(VarStmt var_stmt)
{

}

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The error occurs because VarStmt uses an overloaded operator that takes an argument as a value, and std::visit provides an argument by reference (VarStmt&)